Steam works perfectly on my machine (21.1, previously 20.3), but my partner's machine (20.3) has numerous issues.
There is an option to change the default window on launch (store, library etc), but no matter what I click it stays on store. Often I can right click a game to bring up more options, but clicking on anything in the right click menu just closes that menu and clicks on whatever was underneath it. Games will sometimes launch properly, and sometimes launch for half a second then close without any obvious errors.
I'll let you know if I find anything that causes steam to be more stable.