I'm thinking of catfishing my brother because I missed him
Why would you catfish your brother?
I want to spend more time with him and he is absent-minded.
There seems to be better ways to spend time with your brother. Catfishing is dishonest. Maybe you can reach out to him and say you want to spend more time together?
I have no idea how to talk with him as myself.
Pretending that you're somebody else won't help your relationship with your brother. Try to find something you have in common with him.