Tor Browser is using letterboxing to prevent fingerprinting by screen size.
Now, I have done a test on Cover Your Tracks website from EFF and the results show a unique fingerprint and the reason for that is a Window Size of
1099x999. Shouldn't it be
Edit: My OS did not do the window resize "to fit on screen", and even if it did, the letterboxing should put black borders on the sides so websites can not see the screen size.
Edit 2: It is issue 40081, i am using a high dpi screen. Thank you Peter Gerber for answering!