Tooltip appears below panel when bottom panel above 48 pixels
When the panel is located at the bottom of the screen and the panel height is over 48 pixels, tooltips for launchers, window buttons, notification area, status notifier, pulseaudio, clock, etc. appear below icon.
Distro: Xubuntu 20.04 Theme: Greybird
I had noticed it before and then remembered again today after seeing this link. https://www.reddit.com/r/xfce/comments/hg7j64/cant_read_box_in_panel_how_to_solve_it/