You’re right in that you’d have to install an APK, from outside of the Play Store, however if you’re aware of the right sources of the right apps your security should be fine (you can disable the ability to install apps from unknown sources after you’ve got the YouTube alternative app, without affecting it, if you’re worried about that).

There are a few steps, which are usually straight forward, listed here: github.com/yuliskov/SmartTube

If you follow that link it should have further links for an installation tutorial (they also link a YouTube tutorial to make things easier).

If you do go down that route, it’s a much more pleasant experience imho. No ads, Sponsorblock for in-video ad segments, complete control over quality of video, audio, options to manually force specific codecs, etc.