do nothing: stable version
join beta: future version that is being tested. Should be in beta for 1 week or a little longer, before turning into the new stable version
join alpha: broken and untested, not for players at all. Beta will take parts from the Alpha as they are good enough for release.
you can join the beta, if you want to. But if you dont, it will get to you in a week or so. You decide if you want to risk the unstable version or not.
If you don't mind some sort of instability and possible crashes, go with the beta. So far I'm not having issues but that could change depending on what they pull from the alpha release.
Wow all answers are besides the point.
In steam, right click on bannerlord, go on Betas and there you can choose to opt into the beta. That's also where you opt back out if you want to go back to stable.
Right Click on "Mount and Blade II: Bannerlord" in your Library List -> Left Click on Properties/Funktioner-> Click On Beta-> >You can choose the Beta in the dropdown menu there