Is a facemask considered "overdressed for davening"? Is there a difference between a disposable blue one vs custom made
The mishna brura gives a general guideline of how ones attire should be when davening 90:1
Specifically that one should see themselves standing in front of a king and with awe and dress accordingly.
These days, due to the pandemic, it is perfectly normal to visit the president of the U.S. or the prime minister of Israel with a mask and probably it is enforced.
No reason to assume that it's not appropriate to daven with one on.
What's more, there are those who will consider a person who davens in shul without a mask as a rodef (רודף).