Perhaps it is possible that multiple issues are involved? Looking back at other issues with SQL Workbench causing DBus failures due to missing DBus endpoints could include the fact that SQL Workbench seems to rely on a keyring (be it Gnome Keyring or KDE Wallet). In an issue posted from 2022, SQL Workbench outright fails to connect to DBs in the same manner described if the keyring application isn’t running. It might be worth using KWalletManager to check through your KDE keyring to see if SQL Workbench has been attempting to store and resolve database passwords through your keyring, which won’t be running by default in a plain i3 session.