Josh Johnson ain't done yet -- the 34-year-old QB tells TMZ Sports he's eyeing a big return to the NFL after lighting it up in the XFL this past season.

Of course, JJ was one of the best players in Vince McMahon's org. earlier this year ... starting 4 games and posting a league-best 106.3 passer rating for the L.A. Wildcats.

We spoke with Johnson about his future plans ... and he's ready to get the call to make the leap back to the highest level -- as long as COVID-19 doesn't keep the season from happening.