Giving zakat al-fitr before the prayer is obligatory.

And whoever forgets that, there is nothing upon him except to give it after that, because it is an obligation, so he must give it whenever he remembers.

It is not permissible for anyone to deliberately delay it until after the Eid prayer, according to the most correct opinion of the scholars. Zakat al-fitr is obligatory before the Eid prayer.

And whoever forgets it can make it up.

Whenever he remembers, he can make it up, whether on the day of Eid or after the day of Eid, because this is an obligation, and he forgot it, so he performs it as a make-up, not as an on-time act, because the time for on-time performance has passed before the prayer.

But he performs it as a make-up, and no one is allowed to deliberately give it.

About the time of the Eid prayer.

And if he does that deliberately, then he is sinful and he gives the zakat as a make-up, not as an on-time act.