Hello @sosloow, this sounds similar to #7404. Maybe try going to Steam -> Settings -> Steam Play -> pick a different Proton version in the Run other titles with: drop down list, then pick the Proton version you want to use most often and see if that helps.
@kisak-valve thanks for the tip. I tried to change proton versions there, and I still have the problem.
So, what happened: games that had custom proton version selected got bugged after I upgraded to a new version of ubuntu. I had to re-select that custom version of proton for them, and they appeared as installable.
Nothing extracted yet.
Your system information
Recently I updated to a new Ubuntu 21.10, and some time after that, I noticed that some of the games in my library no longer can be installed. The play button of these games is grayed out and has "available for windows" next to it.
I have steam play enables for all game. Why could this problem appear? I always was able to install any game in my library, even if it has "borked" in protondb.