Earlier quoted context omitted.
To code proofs in lean, you have to understand the proof very well. It doesn't seem to be very reasonable for someone learning material for the first time.
Tao says that isn't the case for all of it and that on massive collaborative projects he's done many nonmathemeticians did sections of them. He says someone who understands it well needs to do the initial proof sketch and key parts but that lots of parts of the proof can be worked on by nonmathemeticians.
This is also the case for other top-profile mathematicians like Peter Scholze. Good luck to someone who wants to put chatgpt answers to random hypotheticals into lean to see if they're right, I don't think they'll have so easy a time of it.