Where is this 'one checkbox'?

There is a search bar in the settings page. Search 'fingerprint', uncheck 'Enable ResistFingerprinting'

I found on 136.0.0-ish that some settings persist despite checking/unchecking that box and restarting LibreWolf, but YMMV. I also manually inspect 'about:config' and search there for relevant settings (like 'fingerprint'). For fingerprinting, browser breakage is unlikely so toggling these hidden flags is easy.