First uninstall your facebook app if you have installed one then download and install the app that I have given below with download link. After installation open freefire and try to login.
I already said on PrimeOSBE that fb access in webview can't be done anymore of course there are exceptions, namely by using chrome as webview ( This method is even easier on PhoenixOS because Xposed works so just install module anywebview ) or using webview + chrome ( Required ).