Mew quest bug ?

[Leafmaster]

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?

[Caennethi]

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/