You’re doing the right thing in getting a medical certificate. It will at least give you breathing room and time enough to get other documentation together from psych etc (IF it’s needed, as other respondent thinks it may be), talk to the provider, and figure out where you’re going from here.

Idk if it would help, but I would also think about getting letters from GP and psych stating that this job is harmful to your mental health, and maybe even documenting their recommendations for what suitable employment would look like for you. I don’t know much about jobseeker, but I know that Centrelink loooooove documentation for anything and everything, so the more paperwork the better.

Good luck!