Samsung says they offer 3 years of updates for the Galaxy Tab S7..but do I follow the S7/S7+ release date of August 2020 or the FE (which is what I have) of may 2021?
Follow what is advertised for the device you have. Even if the Tab S7/S7+ have 3 years, if your Tab S7 FE has only two then you only get two. Same goes for when the updates run through - if the device was released in 2021 and gets 3 years then you get updates through 2024.