Correct Support documentation that incorrectly states there is currently no supported method for setting Tor Browser as your default browser.
On macOS Catalina Version 10.15.3, users of Tor Browser 9.0.4 can set Tor Browser as the default browser:
Apple SSD (or Apple HDD) > Applications > System Preferences.app > General > Default web browser: Tor Browser.app
After a macOS user sets Tor Browser as the default browser, the user can read the following confirmation in Tor Browser:
Tor Browser > Preferences > General > Startup > Tor Browser is currently your default browser