I received the $1,400 stimulus check in March 2021. Got married after. In 2022 I'll file as married filing jointly do I include both of our stimulus checks? Or just mine?

You do not get the $1400 twice.   When you file your 2021 return you will have to indicate that you received your own $1400.   If your spouse did not receive the $1400, spouse may still get it as a recovery rebate credit and it will show up on line 30.   Entering the wrong amount and trying to get the credit twice will put your return in review for months and delay your refund---so get it right.

Yes you will enter what you each got.   I haven't seen it yet but there might be a box for each spouse amount or maybe just the total for both.

Joint is one return combined for the both of you.  You enter all your info and income and hers on the same return.

Your stimulus payment goes on your 2021 tax return, that you are filing now. It's not clear exactly when you got married. If you were married before the end of 2021, you file a joint return for 2021 and you enter the total amount of stimulus payments that both of you received. If you did not get married until 2022, you each file a separate tax return and you each enter only the amount that you received yourself.