I agree, I wouldn’t mention this to your manager OP. I’d just start leaving a few hours early whenever you feel like it/can do it without being noticed.

I’m in a similar position— put in extra work for about a year after being promised a promotion, was told there wasn’t room to promote this cycle, so now I quietly take some half days and spend a lot less time at my desk than I used to.

In my experience, Typescript lets me think significantly less hard because I’m not having to “compile” the types in my head all the time. I think even with no Javascript experience I’d recommend starting with Typescript.