removing FigmaAgent.app
rm -fr ~/Library/Application\ Support/Figma/FigmaAgent.app
creating a dummy file
touch ~/Library/Application\ Support/Figma/FigmaAgent.app
make the file undeletable
sudo chflags -R schg ~/Library/Application\ Support/Figma/FigmaAgent.app
Now Figma will not be able to override that file when it wants to update it and you don’t have to fiddle with the .app everytime Figma updates itself.
Also the login item does not get created for me again after removal at this point.