IRL: I would have to estimate around 120, but 150 or so may be closer. No way to know. I'll say 135.
BoardGameArena: About 50
Androminion: About 100
isotropic (during its glory days): 4677 + sockpuppet accounts probably makes it around 4800
Goko/MF: The client says 12390, but throw in early testing for both Goko and MF and it's +100 or so.
Sock puppet account on MF: 60
isotropic (playtesting days): Estimated 200? Man, I feel like I played more but I probably didn't.
2017 testing: Probably around 30 so far.
So an estimated 17,865. I feel like some large amount of games is missing, though. For one, I am pretty sure I played a lot more games than that on isotropic, but I have no idea how accurate CouncilRoom is (or Goko/MF given the number of disconnected games and such).
Edit: Just saw Qvist's link. I am not sure if the current isotropish leaderboard takes games from that same era into account, but if it doesn't, I can add 4083 Goko games, making the total 21,948.