What you want is NIST 800-63b https://pages.nist.gov/800-63-3/sp800-63b.html#memsecret

Specifically sections 5.1.1.1 and 5.1.1.2.

Excerpt from 5.1.1.2 pertaining to complexity and rotation requirements:

Verifiers SHOULD NOT impose other composition rules (e.g., requiring mixtures of different character types or prohibiting consecutively repeated characters) for memorized secrets. Verifiers SHOULD NOT require memorized secrets to be changed arbitrarily (e.g., periodically). However, verifiers SHALL force a change if there is evidence of compromise of the authenticator.

Appendix A of the document contains their reasoning for changing from the previous common wisdom.

The tl;dr of their changes boil down to length is more important than any other factor when it comes to password security.

Edit to add:

In my personal opinion, organizations should be trying to move away from passwords as much as possible. If your IT team seems to think this system is so important that they need to rotate passwords every month, they should probably be transitioning to hardware security tokens, passkeys, or worst case, password with non-sms MFA.

Now I know nothing about the actual circumstances and I know there are plenty of reasons why that may not be possible in this specific case, but I'd feel remiss if I didn't mention it.