> I'm not making my case "for Trump"
You seem awfully concerned he is being treated unfairly. Maybe you are just a firm supporter of ideological consistency.
> I'm making my case that restricting or banning voting by mail is neither disenfranchisement nor undemocratic.
Then you should pipe down in this situation because he's stated that this is his intention. I agree that restricting voting by mail is not inherently undemocratic although restricting ballot access is almost always going carry disenfranchisement. Regardless, you cannot claim that restricting voting by mail cannot possibly be a means of disenfranchisment, with plenty of very obvious examples. Since we already know that is the goal here, you're using the dumbest possible opportunity to make a pedantic argument. It's like making a case for communism by talking about how great Kim Jong Un is.
> I think it's very material that no or minimal criticism about voter disenfranchisement was levied at those other countries on this basis
If you're making a definitional argument then the status quo is immaterial. If you are worried about poor Trump getting unfair treatment, it's a worthwhile thing to point out. But you aren't doing that! Just make sure you note which countries restrict vote by mail using partisan chicanery with the goal of keeping power.
> If you want to argue Trump is breaking the US constitution in enacting these changes, be my guest. But something is not democratic or not based on whether it abides by the US constitution.
I never claimed the US Constitution determines whether or not something is democratic outside its borders. In any venue, for something to be democratic it ought to follow the rule of law.