You could use a throwaway email and signup for an account. The account creation is a little tricky if you don’t use a “real name” but a name generator website may help in this, or use a combination of two tv character names.
Also use a privacy oriented web browser that signs you out each time, something like mule for android or librewolf for desktops.
One thing not to do is use the FB app or the messenger app on your phone, instead do everything on a browser.