I tried the above fixes and nothing, but then I came across this one that worked for me:
viewtopic.php?f=3&t=212141"1. Removed the "Blackmagic Desktop Video Driver Extension" under the Driver section.
Click the three dot button and choose "Delete Extension"
https://support.apple.com/en-gb/guide/m ... usr003/mac
2. Some of these Agents and Daemons was not properly deleted during the Unistall.
So I manually delete the LaunchDaemons and LaunchAgents
/Library/LaunchAgents/...
com.blackmagic-design.DesktopVideoUpdater.plist
com.blackmagic-design.DesktopVideoDriverExtension.plist
com.blackmagic-design.DesktopVideoDriverExtensionRemove.plist
/Library/LaunchDaemons/...
com.blackmagic-design.DesktopVideoHelper.plist
com.blackmagic-design.DesktopVideoDriverExtension.Helper.plist
3. Ran the Uninstall Desktop Video.app
4. Rebooted
5. Reinstalled Desktop Video Setup 14.2.1
6. Reboot and Authorised the Extension (or if it was the other way around)
7. Launched Desktop Video Setup
8. Connected the 3G Recorder and after a few second it was identified by the Desktop Video Setup
Disconnected it and treid the 3G Monitor instead and with a few seconds the Monitor device was identyfied as well.

"
I hope this helps.