What is the difference between Beta and Alpha program?

Alpha updates are not automatic and you need to sideload them as it was, previously, for the beta.

Alpha is considered less stable and more buggy(in the case of the latest updates for example the UI was a bit buggy with incomplete informations and data regarding the new features).

You can find the instructions in the following forum https://forums.garmin.com/beta-program/fenix-7-series/f/announcements

Keep in mind that the actual alphas are what was considered, previously, beta and the actual beta is what was considered an RC release(pretty much ready for final release let's say). 

If you like to test new stuff consider installing the alpha as you will get new features earlier and, while it's true that they can be incomplete, you start to gather data much earlier. For HRV baseline for example you need 19 days of readings and people that installed the first alpha got it already while the feature is not even officially released.

Personally, i never had critical problems after installing any alpha or beta but it could happen that something goes wrong and that you need to backdate the software and lose some settings or worst.

I would say that it's better if you take a look at https://forums.garmin.com/beta-program/fenix-7-series/f/community-discussion or https://forums.garmin.com/beta-program/fenix-7-series/public-alpha-bug-reports/i/public-alpha-9-xx

Nothing that impacted my usual activities...only stuff related to the new features.

I'm on Android but on iOS there were some issues with sync(with workarounds too) between the watch and Connect.

thank you very much, I am also with android