Man, for a console gamer coming over this thread has a bunch of pretty terrible recommendations. I can't imagine a better way to send somebody back to console gaming than immediately dumping a bunch of fiddly mods and janky old stuff on them so they can play their OS for a while before having any fun.
I mean, if they're into competitive, hardcore console stuff they probably will want to decide if they want to go down the rabbit hole of competitive PC gaming. Checking out a couple MOBAs or fast mouse and keyboard shooters is probably a good way to start (for Steam ease of use I suppose DOTA2 and CS2 are the obvious choices). That's the fighting game equivalent stuff they're unlikely to have played already. I'd say if they aren't feeling it, it's fine to step away, though.
Depending on how beefy their gaming PC is, it may be fun to go for crazy console-crushing visuals. Path traced games like Indiana Jones or Cyberpunk may be fun to check out even if they've played the console versions, if they have a current-gen expensive GPU in there.
There are a couple of genres that are also cross-over but play best on PC, like survival sims and the like. I'm a PC controller player, but I'll switch to mouse and keyboard for, say, Satisfactory, although that's less action-packed and timing-based.
And of course there's upcoming stuff. VF 5 REVO is coming out in January, and that seems like a good chance to jump into a new thing on a gaming PC instead.