I think it was a Korean novel where the main character was a returnee and later in the novel his dad also apparently returns and is in the US and some ass is brought in to confirm if he is actually a monster and sets the father off to beat them all?
Sounds like Solo Leveling, though the MC technically didn't leave? But the Father returning to the US sounds exactly like it. or alternatively I Alone Level-up (They are the same just different names for same things.
Seoul’s station necromancer (father doesn’t return, but the novel is a good one if you liked the suggestions above)
it might be Everyone Else is a Returnee, as the father returns.... K...if it sounds like a stretch, its because it is.............. I also think its Solo Leveling (Or I Alone Level Up), as the father returned in the US... he isn't a returnee though, since he never left...?
Solo Leveling (there aren't any returnee) MC got the system upgrade and OP MC Father trapped in Dungeon and after he had beaten them all monsters in there, he came up to the exit which's somewhere in Canada bordering US place kind of place. Because there're high fluctuation of Magic (mana) there (opening Dungeon exit) so US hunter searching in there and found a rouge man with long hair and beard like beggar who ain't bath over 10 years somekind like that and fight and defeat all