While with most of them you get what I would call "vanity metrics" (so not really actionable, more or less just "numbers go up or down") at least Matomo (self hosted) provides the ability to create essentially the experience of a free GA3 implementation.
If you "just" had a code drop of basic GA3 code: just use whatever floats your boat. If you have custom dimensions, user interactions tracked as events, goals and stuff like that in the free GA3 version - go with Matomo (self hosted). Configure Matomo to have more than 5 custom dimensions (easy to do) and you can replicate (nearly) everything from your GA3 implementation.
Only things you will be missing in any case is integration with Search Console and Google Ads.