Hello I’m new, I don’t know if this is the right place to ask for help.
The message is translated by a translator because I am bad in English.
I captured and saw all the pokemon of kanto only the 3 legendary birds and Mewtwo not capture but they are seen by pokédex.
When I talk to Professor Oak he tells me that it is not enough.
Can you help me solve this problem?

If you could tell us how far into the Mew quest you are so far, we can probably help you better.

Did u already get the Dragon Membership, unlocked Cerulean Cave and fought Mewtwo to get Seen Data?

Here is a guide for the quest:
https://pokemonrevolution.net/forum/topic/8037-how-to-get-mew/