@jul I'll check why you're having difficulty with that and post back. As the addon runs completely off of template modifications and CSS, there should be nothing left over after uninstall.
Just as an update on things, this addon isn't abandonded but yes it may seem so. I haven't made a larger community statement on this but I have been in consideration of leaving the Xenforo space due to how the past 6 months (and losing staff/team) left me with no time to adequately support products to a sufficient degree as a one-person team. Support channels were pulled to tickets only just to consolidate things. In such a decision, my products would be handed over to another developer.
Essentially, I'd love to stay with Xenforo development if there's a valid path forward and I can recuperate the whole situation with support and general wanting of my products. There's in fact a massive amount of unreleased work that I feel would be a shame to not finish and release (including this addon).
For anyone still interested in XenPorta Improvements, you will be seeing an update on this. Otherwise I understand moving on to other choices.
Hey @jul if you're still having trouble, please send me a pm with a screenshot so I can take a look. No issues so far running test uninstalls, it's possible you may have some modified templates or Style Properties that need reverted.