So, I was having a hard time trying to update Nobara 38 to Nobara 39. Did the KDE swap, followed the website instructions to upgrade but in the last part, after:

$sudo dnf system-upgrade download --releasever=39 -y

I'd get:

Error: Transaction test error:

file /usr/lib64/libopenh264.so.2.3.1 conflicts between attempted installs of noopenh264-0.1.0~openh264_2.3.1-2.fc39.x86_64 and openh264-2.3.1-2.fc39.x86_64

Tried several solutions to this without success but noticed it's just that two packages in the upgrade are trying to write the same file. My solution was to just disable the openh264 Cisco repo for the upgrade with:

$sudo dnf config-manager --set-disabled fedora-cisco-openh264

You can do this also in the Diskover preferences.

After disabling the Cisco repo you can proceed with:

$sudo dnf system-upgrade download --releasever=39 -y

$sudo system-upgrade reboot

Then, after a successful upgrade, go to Diskover > Preferences and enable (check) the fedora_cisco_openh264 repo. Finally, do perform a system update with Nobara update tool. Install whatever it tells you it's missing and then you are done.

Figured I'd share this here since the threads in Reddit don't show any clear fix to the problem. Hope someone can use it.