I can confirm the bug with some different behaviour:
1) The "Authentication Import key file..." dialog opens, a file can be selected but the key is not importet
2) Startet in a sudo terminal I do not get any messages
3) No other standard key is shown
4) "Other Software Add..." is also not importing sources
tested with: 22.04 Mate software-properties-gtk 0.99.22 software-properties-gtk 0.99.22.1
I can confirm the bug with some different behaviour:
1) The "Authentication Import key file..." dialog opens, a file can be selected but the key is not importet
2) Startet in a sudo terminal I do not get any messages
3) No other standard key is shown
4) "Other Software Add..." is also not importing sources
tested with: properties- gtk 0.99.22 properties- gtk 0.99.22.1
22.04 Mate
software-
software-