Opening links to Microsoft Teams meetings from Thunderbird/Lightning would launch in Firefox and then open in the Microsoft Teams for Linux app just fine before upgrading form openSUSE 15.1 to 15.2.

Now the same action instead triggers an error notification from KIOExec: "Unable to create io-slave. klauncher said: Unknown protocol 'msteams'.

I figured out a workaround today and no longer have the process die at a KIOExec error. I manually selected teams as the default application in Firefox. Firefox now shows "Use teams" as the action, but it is still has an option available for "Use Microsoft Teams - Preview (default)"

I just looked at protocol handler settings for "Bittorrent Seed File" and see it similarly configured with an entry that I did not create for the exact same program that is manually selected set as the active default, so maybe my workaround is the only real fix.