I had a problem with the tray icon for Flameshot (Prt sc) not displaying properly when I boot. It showed an icon that was too small compared to the other seven I have. Adding a delay, I gave it 10s, to it's .desktop file (/.config/autostart/Flameshot.desktop) fixes this.
Add this line to the end of the file using whichever txt editor you like.
If you need a delayed start for apllications that may be starting too soon this should work.
I'm running MX23.4_ahs w/6.10.11-2 liqourix kernel & XFCE.