Let’s fix each of these, starting with the most effective solution.
: Temporarily turn off your firewall or antivirus, enter the key, and then turn it back on.
: Update to DaVinci Resolve Studio 19.1 or newer. Blackmagic Design released these updates specifically to address the "activation loop" on newer macOS versions.
: Entering your key on a machine when you've reached the limit will "steal" the license back from previous machines and reset the internal counter. Manual Deactivation