Hi,
I have installed your Favorite Items plugin on localhost for test {PHP7.3}
In admin, the theme "Appearance" menu move to top and "theme settings" don't show anymore after activating the Favorite Items plugin !!
I have tried with Bender theme and same result ...
For information, I have installed Osclass 3.9.0
We can find different version of Osclass on the net ... including the version 4 !!!
Thank you,
Chris