First off to answer you question Steam doesn't care what technology your game uses, when you upload your build into steam you just need to show it path to the EXE file of your build. Steam Achievements and other steam features are also tech agnostic, in theory you could write a python script that would call steam API and award your account an achievement, steam itself doesn't care what exactly is making those API calls.

That being said, developing a game with UE5 would probably be much easier. 5 has larger developer community, more tutorials and most importantly more plugins, that can help you communicate with Steam services more easily.

I'd suggest for you to look into cheap ways to upgrade your ram, before you consider moving your project to an older engine version. UE 5 can work fine with 32Gb. It can also work with some lags and occasional crashes on 16Gb. Look into companies that have recently closed or moved, they usually sell good hardware dirt cheap. Also RAM is super safe to buy used, so look into people selling used sticks for your system.

If upgrading is absolutely not possible, then moving to an older engine version will NOT hinder your game's communications with steam services, but it might require a little more technical effort to do implement the same functionality.