M1 Mac Mini: Unable to install driver for audio interface on External boot drive.

M1 Mac Mini: Unable to install driver for audio interface on External boot drive.

I have created a bootable external NVME drive of Big Sur which i use & works great with one frustrating exception: I use an RME audio interface which has an M1 driver (which works great when installed on the internal drive of the mac mini. (the security permissions on both the internal & the external drives are set to "reduced" and "allow kernal extensions..." When i try to install the driver on the external Nvme drive , the installer runs BUT I dont get the "blocker" which should appear so you can select "allow" under Systerm Preferences > Security & Privacy > General. When i restart the system the interface does not show... I think the issue has something to do with the fact i am installing to an external boot drive and Big Sur has 2 partitions (OS & Data). Have tried with system protection on & off...