Why would a professor not reply?
Given that the 20 or so days covers holiday periods there might be a simple answer. The professor might be traveling. Might even be sick, given the pandemic. You can follow up if you like, but keep it polite. If you have access to the department email address, you could ask them if there is a reason that they might not be replying.
Don't jump to conclusions, but follow up with other options that you have.