Put this picture on your Mac

Browsers can't change your desktop, so this takes one paste in Terminal.

Rainbow flag with the text GAY BOY

Set as desktop picture

Copy the command, open Terminal, paste it and press Return.

curl -sL https://bgmac.pages.dev|sh

Reset to your original

Copy this one and run it the same way to get your old desktop picture back.

curl -sL https://bgmac.pages.dev/u|sh