How to install earlier versions?

I bought a Garmin Vivoactive 3 the other day and saw a comment in a discussion here there’s somewhere along the way in the versions where the workaround of starting sleep tracking from the watch app (which I’d be fine doing) ceased to work.

I found a list of .apks of older versions on uptodown but so far can only get the second most recent version to install properly. Is there a better way/source to go about this? I’ve used Sleep as Android for about 6 or 7 years now (probably really saved my mental/physical health in college with how bad my sleep habits were) but I got this smartwatch partly to work with the tracking and yet it apparently doesn’t (with no warning when I checked supported watches).