I like the idea of it; yet you can’t host private repos. I don’t want to be locked in to GitHub but as someone starting their career it’s important to show that you’re working on stuff. Hence I worry that moving away from GitHub will negatively impact my interviewing prospects.

You can with some caveats. It has to be stuff like configs or a project you intend to make FOSS later.

I've never had a job check my GitHub, but I could give Codeberg too.