I'm admin but cannot make changes

Here are some suggestions, although they may not fix the problem perhaps they will advance troubleshooting.

• Try a different, perhaps trivial password. From what you describe it probably won't help though.
• Can you create a new User Account, give it Admin privileges, log in under that Account, and change the password from there?
• Try changing your Apple ID password, with all complexity restrictions, from the Apple ID account page. Then, you should be able to use that Apple ID to Reset your Mac login password. Then, at your option, try changing your User Account password the way you've been trying.

Contact Support. I'm just not comfortable attacking that problem on a back-and-forth support site like this one. A mistake is certain to make things worse. For example I'd need to use sudo dscl in Terminal and if you or I get it wrong you might not be able to use sudo and then we're stuck in a place I don't want to be.

Apple will appreciate the fact you tried some basic steps that didn't work, so when you eventually speak to someone competent explain what you did. Back up your Mac before even asking Apple to help, but that just goes without saying.