Iirc Gary caught over 200 Pokémon of 60 different species. Depending on how you look at it you could say Ash just needs to get to 60.Over 1000 episodes and yet he never made it past Gary's OS caught Pokemon numbers.
Going by the 57 Pokémon on the final poster plus Beedrill, Seaking, and Raticate Ash does have 60. Though unlike The 57 I don’t see those three coming back for a team photo.
Now counting Pokédex space count so Pikachu and his evolution line would for example take three slots for himself, his pre-evolution, and his evolved form. It could be said technically Ash has…
Kanto: 32 (39 with the fish, bee, and rat, but I’d rather not count them)
Paldea: 1 (Annihilape)
Total: 137 (144 with the previously mentioned trio)
…okay either way he is still pretty close to 150 and it would be kind of funny if Ash caught enough Pokémon that if you count their entire evolution lines you could say that Ash caught his own 150.