I've created a custom archiving policy that should archive emails older than 2 months and assigned the policy to selected folders.

1 day later, none of the emails to which the policy should have been applied got archived. I understand that the emails would/might not get archived immediately but is there some rule when the archive policy is actually applied?

The only other related post that I found is 7 years old so it's not clear whether it's still relevant but most of all it seems to imply that archiving is applied based on the account storage level which I have trouble believing because this doesn't seem to be documented anywhere and would be extremely unintuitive.