I was trying to change my master password today via the Preferences dialog in the Mac app... I typed a really long password (twice) and still got the message "That's too short. Your password needs to be at least 10 characters to keep your secrets safe."
I think the issue is I had a ' (apostrophe) fairly early in the string - it seems like if you do this, no matter how many characters you type subsequently, the "10 characters" message does not go away and the "Use This Password" box remains greyed out. Other punctuation doesn't seem to cause this issue, although I'm not sure if I did an exhaustive search. I also didn't try changing it via other mechanisms, so it may be more than just the mac app.
But, now that I've disclosed this I also need to think of a new password without a ' in the first 10 characters.
1Password Version: 7.9.2
Extension Version: Not Provided
OS Version: macOS 11.6.2