If applicable, where is the list of open tabs stored?
I just tried Zotero 10.0.2-beta.2 on Ubuntu 22.04 and it closed all my tabs. I have a backup of the Zotero data directory, so is there a way to restore a configuration file to restore all the lost tabs?
Upgrade Storage
I don't think there's anything in the beta that would've caused this. Are you running any plugins that interact with tabs?
I only have BBT and Zoplicate running. I don't think they interact with tabs.
The only thing that happened is Zotero telling that the database was created by a more recent version of Zotero and that the beta needed to be updated, which I agreed for. After restarting, the tabs had vanished.