Is it closed due to lockdowns?

Yes.

Foodland is the only place open.

The Gourmet Market on the basement floor is open.

all malls are closed except for the supermarkets and  pharmacies ,not sure about banks.

1 hour ago, bkk6060 said:

Foodland is the only place open.

There isn't a Foodland in Terminal 21, Bangkok. It's a Gourmet Market (but it is open).

I dare you to walk around an empty terminal 21 with Herbert Chappell - The Gonk on the headphones  ? ????

 

 

 

24 minutes ago, brewsterbudgen said:

There isn't a Foodland in Terminal 21, Bangkok. It's a Gourmet Market (but it is open).

There is a Foodland in Soi 5 and another one in Soi 16. They are open.

8 minutes ago, OneMoreFarang said:

There is a Foodland in Soi 5 and another one in Soi 16. They are open.

Correct. All supermarkets are open. However the OP was asking about Terminal 21, where there is a Gourmet Market. 

Depends on your definition of closed. 
 

Technically, Terminal 21 is open. I was just there yesterday. You can walk in and walk around. A few stores inside - like pharmacies - are still open. For example, you can take the escalator down and buy stuff at Watsons or Boots. I just bought some masks there. Some ATM’s and bathrooms are also open/functional inside the mall. 
 

Same story with Emquartier and other big malls.