Is there any way to set more than 20 character PIN for Bitlocker?

There is the “enhanced pin” option in group policy but while that allows letters and symbols etc., the max length is still 20. This is impractical for using passphrases as they would be far too short to be secure.

Seems like you can’t :

PINs/enhanced PINs will not allowed to be longer than 20 characters, by the way.

But you can use a… password, which can be up to 256 characters long. Just use your passphrase and you’re good to go.

Another thing that could help you :