I’ll be moving your post to the Support and Help area.
I’ll also suggest you provide some pastes giving details, eg.
lsb_release -a; lxqt-about --version
The release-upgrade from 24.04 to 26.04 isn’t yet open, so how exactly did you perform the release-upgrade.
There is a known issue (read about it here) where the update is being offered too early (it’s been offered because 25.10 to 26.04 was open, but shouldn’t have been seen by users of 24.04). I wonder if you saw & tried to accept that, thus you’re still on Lubuntu 24.04 LTS.