Does the latest revision of Argon ONE M.2 have out-of-the-box trim support?

ARGON ONE (V2 and M.2) DISCUSSION
1

And then does Trim work automatically or do you have to do it manually?

2

trim support for the Raspberry Pi needs to be done manually.

https://www.jeffgeerling.com/blog/2020/enabling-trim-on-external-ssd-on-raspberry-pi

you may follow the link for instructions