elive-upgrader has been updated with some improvements to incrase these "minimum space for backup" numbers... hopefully working better for the next time
ok let me understand... so the upgrade worked fine in everything and the problem was when starting the graphical system ? (yes this can be because of the nvidia drivers... the tool has not the privative nvidia drivers featured, I should implement it... 
you can actually run the installer of the privative nvidia drivers in any moment in elive, you just need to boot your system and having access to a console tty (no graphical system) where you can install them with the elive tool to install nvidia drivers
that should be for the backuping of the system
known bug for the DISPLAY variable afecting mulitple apps, it took me a while but its fixed now if you "apug" your system 
interesting, smplayer works for me
UPDATE: yeah seems like your system was broken, as we can see:
the strange thing is that your system "correctly" upgraded but was left in a broken state, why?...
you have LOGS in your /root about the upgrade, check them, there should be the reson in there, so its important to know what happened in order to solve it
forky detection was a bug checking the existing elive repository for that version: fixed
_note: for this case, it will tell you that there's no new versions to upgrade because you are already in trixie, its just that your system upgraded broken... we need to see what happened in your logs
question: so does elive-upgrader restored to bookworm correctly ? (never tried that feature in fact)
I know this, it was an issue in e16 that I was working for a few days but it was finally fixed, the -actual- packages should work without issues now, you still have the issue ?
Seems like you were doing tests while I didn't finished to work on elive-upgrader to make it working the previous week 
, thats why it worked that time...
Since you mentioned "feeling slower" and have this strange graphical bug, I assume the problem is with the nvidia drivers... try to install the privative drivers? I think this howto should be summarized but you have it here (basically boot without graphical system and run the tool, everything is guided): Nvidia Privative Drivers installation . Keep me updated for the nvidia drivers (not implemented yet in elive-upgrader)
So, do we have the plymouth bug ? I didn't tried the upgrader since the last time i made it working around 1 week ago (anybody can do its betatest in virtualbox too), I should finish to implement a few things and do a new betatest