You might be smart

Smart-arse more like. A serial troll who doesn't actually know what they're talking about.

This kind of problem falls under “communicating badly and acting smug when misunderstood”.

No it doesn't. It falls under adults forgetting the rules of Maths.

Use parenthesis and the problem goes away

There is no problem, other than adults who have forgotten the rules.

You understand that gen x starts around 1965, right?

10 years earlier than that actually. Johnny Rotten, Billy Idol, etc. The U.S. came late to the party and started using their own definition.

For me it’s the arguments when there is a parentheses but no operator (otherwise known as implied multiplication)

No, it's known as Factorised Terms/Products, solved via The Distributive Law, a(b+c)=(ab+ac). "implied multiplication" is a made up rule by people who have forgotten the actual rules, and often they get it wrong (because, having wrongly called it "multiplication", they then wrongly give it the precedence of multiplication, not brackets).

Where I live, this would be considered juxtaposition

Not just where you live, everywhere, in Maths textbooks. Adults forgetting the rules (and unqualified U.S. teachers not teaching what's in the textbooks) is another matter altogether.

There’s no “whatever-the-fuck-your-country-calls-it”

Yes there is. BEDMAS, BODMAS, and BIDMAS

the US is the only country using it

No they're not.

at some point they’re dropping it

No, at no point do the order of operations rules ever get dropped

using multiplication by juxtaposition (2x + 4x2)

They're called Terms/Products.

Hey, this is Presh Talwalkar

Person who has forgotten about The Distributive Law and lied about 1917.

Discussion of a brief history of this viral math problem

Including lying about 1917

Ultimately followed by brief discussion on the order of operations

But forgets about Terms and The Distributive Law.

And that’s the answer

Now watch his other ones, where he screws it up royally. Dude has no idea how to handle brackets. Should be avoided at all costs.

So order of operations is hard?

Not for students it isn't. Adults who've forgotten the rules on the other hand...

The issue normally with these “trick” questions

There's no "trick" - it's a straight-out test of Maths knowledge.

the ambiguous nature of that division sign

Nothing ambiguous about it. The Term of the left divided by the Term on the right.

A common mistake is to think division is prioritised above multiplication

It's not a mistake. You can do them in any order you want.

when it actually has the same priority

Which means you can do them in any order

Right to left:

6 * (4 / (2 * (3 / 9)))

Nope! 6 × 4 ÷ 2 × 3 ÷ 9 =4 right to left is 6 ÷ 9 x 3 ÷ 2 × 4 =4. You disobeyed the rule of Left Associativity, and your answer is wrong

Multiplication first: (6 * 4) / (2 * 3) / 9

Also nope. Multiplication first is 6 x 4 x 3 ÷ 2 ÷ 9 =4

Left first: (24 / 6) / 9

Still nope. 6 × 4 x 3 ÷ 2 ÷ 9 =4

Right side first: 24 / (6 / 9)

Still nope. 6 × 4 x 3 ÷ 9 ÷ 2 =4

And finally division first: 6 * (4 / 2) * (3 / 9)

And finally still nope. 6 ÷ 9 ÷ 2 x 4 x 3 =4

Hint: note that I never once added any brackets. You did, hence your multiple wrong answers.

It’s ambiguous which one of these is correct

No it isn't. Only 4 is correct, as I have just shown repeatedly.

Hence the best method we have for “correct” is left to right

It's because students don't make mistakes with signs if you don't change the order. I just showed you can still get the correct answer with different orders, but you have to make sure you obey Left Associativity at every step.

I stand corrected

No, you weren't. Most of their answers were wrong. You were right. See my reply. 4 is the only correct answer, and if you don't get 4 then you did something wrong, as they did repeatedly (kept adding brackets and thus changing the Associativity).

until the ambiguity is removed

There isn't any ambiguity.

all those answers are correct

No, only 1 answer is correct, and all the others are wrong.

Until the author gives me clarity then that sentence has multiple meanings. With math

Maths isn't English and doesn't have multiple meanings. It has rules. Obey the rules and you always get the right answer.

it doesn’t click for people that the equation is incomplete.

It isn't incomplete.

100% with you. “Left to right” as far as I can tell only exists to make otherwise “unsolvable” problems a kind of official solution

It's not a rule, it's a convention, and it exists so as to avoid making mistakes with signs, mistakes you made in almost every example you gave where you disobeyed left to right.

It’s so we don’t have to spam brackets everywhere

No it isn't. The order of operations rules were around for several centuries before we even started using Brackets in Maths.

((((((9+2)-1)+6)-4)+7)-3)+5

It was literally never written like that

we only need parentheses when we want to deviate from the norm

That has always been the case

The solution accepted anywhere but in the US school system range from “Bloody use parenthesis, then” over “Why is there more than one division in this formula why didn’t you re-arrange everything to be less confusing” to “50 Hertz, in base units, are 50s-1”.

No, the solution is learn the rules of Maths. You can find them in Maths textbooks, even in U.S. Maths textbooks.

so no actual mathematician, or other people using maths in earnest, use that kind of notation.

Yes we do, and it's what we teach students to do.

Addition first:
9-4=5

Nope. Addition first is 9+3-1=12-1=11. You did 9-(1+3), incorrectly adding brackets and changing the answer (thus a wrong answer)

Except it does matter

No it doesn't. You disobeying the rules and getting lots of wrong answers in your examples doesn't change that.

I left some examples for another post with multiplication and division

Which you did wrong.

I’ll give you some addition and subtraction to see order matter with those operations as well

And I'll show you it doesn't matter when you do it correctly

Subtraction first:
1 + (2 - 3) + 4
1 + (-1) + 4 = 4

Nope. Right answer for wrong reason - you only co-incidentally got the answer right. -3+1+2+4=-3+7=4

Right to left:
1 + (2 - (3 + 4))
1 + (2 - 7)
1 + (-5) = -4

Nope. 4-3+2+1=1+2+1=3+1=4

Edit: You can argue that, for example, the addition first could be (1 + 2) + (-3 + 4)

Or you could just do it correctly in the first place, always obeying Left Associativity and never adding Brackets

in my opinion that’s another ambiguous case

There aren't ANY ambiguous cases. In every case it's equal to 4. If you didn't get 4, then you made a mistake and got a wrong answer.

Oh, but of course the statement changes if you add parentheses

It sure does, but they don't seem to understand that.

Another common issue is thinking “parentheses go first”

There's no "think" - it's an absolute rule.

then beginning by solving the operation beside them

a(b) isn't an operation - it's a Product. a(b)=(axb) per The Distributive Law.

(mostly multiplication)

NOT Multiplication, a Product/Term.

The point being that what’s inside the parentheses goes first, not what’s beside them

Nope, it's the WHOLE Bracketed Term. a/bxc=ac/b, but a/b( c )=a/(bxc). Inside is only a "rule" in Elementary School, when there isn't ANYTHING next to them (students aren't taught this until High School, in Algebra), and it's not even really a rule then, it's just that there isn't anything ELSE involved in the Brackets step than what is inside (since they're never given anything on the outside).

÷ could be a minus sign

No it couldn't.

Division sign - Wikipedia

(en.wikipedia.org)

Did you check the reference? It says % can be used as a minus sign, not the obelus. Welcome to what happens when you're next-door neighbour Joe Blow can edit Wikipedia.