Does My seaplane rating expire? What is the regulation on Recurrent?
 

Hi, I got my seaplane rating in March 2020, but the chance of flying seaplane again is so small, and I am wondering does my seaplane rating expire?
Also what is the regulation on recurrent, is it to do 3 takeoffs and landings to carry passengers again?
Thank you.

No, it doesn't expire, but you need a BFR every two years. And as you said 3 t/o's and landings in the last 90 days to carry pax.
And a medical, of course.
Check FAR 61

3 takeoffs and landings in the same category (Airplane), class (Single Engine Sea), and type in the last 90 days to carry passengers. The Flight Review can be in any category/class you hold.