When I opened Steam after installing Mac OS Big Sur Beta for the public I couldn't play my game. I detailed below how I resolved my issue step by step for those who prefer a detailed explanation.
(IF YOU JUST NEED TO KNOW THE STEPS WITHOUT ALL THE DETAILED DIRECTIONS SCROLL TO BOTTOM OF THIS REPLY) I hope this is helpful.
Open the Steam application, select from the menu bar at the top,
Steam->Preferences. The Preferences window opens to
Account tab selected from the sidebar on left by default. On the right side your account information and options for account security, change password, and change email are displayed, below these options you will see the option
Beta participation: Select the box that says CHANGE... This will open a new window read the short explanation about beta participation, below is a drop-down menu with the options
NONE-OPT out of all beta programs or
Steam Beta Update, select drop-down menu and Choose Steam Beta Update, Click OK. The app will notify you Steam must restart.
Confirm restart. If Steam does not restart on its own open it manually. Check to see if your games are playable, your games should no longer be grayed out. I hope this helps out!
If you still are having issues I would first check for any new updates
(Select Steam in the menu bar the option Check For Updates… is below Preferences in the menu) If updates are available install and restart app. Check to see if the problem was fixed. If that does not resolve your issues send feedback to steam as well as apple, include details of your issue and steps you have taken to resolve the issue.
(These issues are to be expected when using any beta version of a program or OS that is why feedback is so important the better the feedback the quicker these issues can be resolved.)
( I ONLY HAVE USED STEAM TO PLAY KNIGHTS OF THE OLD REPUBLIC II AND DOING THIS FIXED THE PROBLEM FOR ME. I WILL ADD AN UPDATE IF I RUN INTO ANY ISSUES IN GAMEPLAY, BUT SO FAR SO GOOD. I CAN'T VOUCH FOR HOW WELL THIS WORKS FOR OTHER GAMES SINCE I HAVE NOT PLAYED ANYTHING ELSE.)
Here is a quick instruction for anyone who doesn't need every step explained. LOL!
1) Open Steam App...
2) In the menu bar at the top select->Steam->Preferences
3) Account tab should be selected by default from the sidebar (on left)
4) On the right side you should see account information and some options for account security, change password, and change email. Below those options, you should see Beta participation: displayed with a selection box that reads CHANGE… Click on this box to open a new window with a message and a drop-down menu.
5) Click on the drop-down menu and select Steam Beta Update from the two options available, press OK to confirm your selection and receive the beta update for Steam.
Instructions if You Are Using Big Picture Mode:
Select 'Settings' then 'System'
Check the ‘Participate in client beta’ option
Follow the prompt to restart Steam
Steam will alert you the Application needs to restart once the beta updates are installed, confirm to restart the
app. (If it does not reopen on its own reopen the app manually) Check in your Library your games should now be playable. If you run into any bugs or issues, send a feedback report to both Steam and Apple with details of your issue. Hope this helps!
~Martha ;)