can i add memory to my mac air m1 from 8 to 32

In addition, the only way to upgrade is to trade in (or sell privately) and buy a new one and all M1 Macs are limited to 16GB max.

If you really require more than 16GB you will need to buy one of the new MacBook Pros.

As far as I can remember, the MacBook Air line has never had user replaceable RAM.

No. RAM is integrated into the processor. You can't add RAM.

Only at time of purchase; not post purchase.