You can disable the security feature temporarily with "sudo spctl --master-disable", allow SC to boot the ugens, then re-enable it immediately afterwards with "sudo spctl --master-enable". This seems to work OK.
But if you prefer to go about things more carefully (by which I mean, NOT disabling the global security mechanism even briefly), this seems to work on OS X Big Sur:
As SC tries to load each ugen, it shows a dialog saying unidentified developer, etc., and suggests moving the ugen file to the trash, or allowing you to cancel.
Cancel the first one, then go to System Preferences > Security & Privacy where you'll see its name mentioned at the bottom of the dialog, something like "MiRipples.scx was blocked from use because it is not from an identified developer."
Next to that text is an "Allow anyway" button. Click that, then return to the next dialog that OS X put up saying that the next ugen was forbidden, and repeat the process.
Once all of them have been given "Allow anyway", if you boot SC again and load the ugens, you will still get dialogs asking if you really want to open each one. But you can say Open, and after that, everything seems to work fine.