Assalamu alaykum wa rahmatullahi wa barakatuh, Is it the asl that every Muslim is considered to be from Ahl al-Sunnah wal-Jama‘ah (or Salafi or any other of its many names)? Jazakum Allahu khayran.

Yes the ulama mentioned this, as sheikh Alfawzan and others. The mufti of Mecca sh Muhammad Bazmol mentioned that the basic principle is that every Muslim is a Salafi, because the meaning of Islam is to follow the Messenger ﷺ, to adhere to him, and to adopt what came from the Companions in matters of religion — this is the foundation. However, not every Muslim remains upon this foundation, so not every Muslim is a Salafi. A Muslim may fall into things that contradict what the Messenger ﷺ and his Companions were upon, yet that does not necessarily take him out of Islam.