It appears there is a apparmor configuration issue with Transmission on 25.10. See launchpad bugs Bug #2127486 “[Ubuntu 25.10 Questing] Transmission (BT Client): ...” : Bugs : apparmor package : Ubuntu and Bug #2125314 “Transmission-QT fails to start properly due to Ap...” : Bugs : apparmor package : Ubuntu
Hi,
Since 25.10 is now released and no longer in development I moved your post to the correct category.
Please note that while we do appreciate efforts to inform the community, this is not the correct place for reporting bugs.
Thanks.