We have just shipped an updated Steam Client to the Preview/Beta channel.
General
Allow changing account while a game is running. In this case, the change account dialog shows a warning that proceeding will close active games.
Steam shutdown now waits for just-exited games to finish cloud sync.
Added "Ask which account to use on startup" toggle to startup account chooser.
Eliminated "change account" confirmation dialog in most cases. Changing account while Steam is running now brings up the account chooser directly, then restarts as the chosen account.
Downloads
Fixed local game transfers no longer working.
Fixed Proton games with mixed case paths failing to install or update with Disk Write Errors.