Just to update. Tried a Sabrent one and that suffers the same. Emailed Sabrent and they advised, ‘If you are using BigSur version 11.2 or 11.3.1 The issue is related to the software in your Mac M1 computer.’
That sounds unusual. I have an M1 Mini and have been able to connect at least 6 external USB drives with a variety of enclosures. There *are* issues with the connection speed that is recognized, i.e. I have a USB 3.1 Gen 2 enclosure that supports 10Gbps but only connects at 5Gps.
I also have Samsung T5 and T7 drives, which connect at 10Gbps and have no problems.
The problem is *likely* to be the controller in your enclosure - you need to find the type of controller chip and search for known issues. A secondary possibility is that there is an issue with the NVMe to USB driver... all of my drives in 3rd party enclosures are SATA III.
Other things to consider:
1) Is your disk otherwise healthy?
2) Have you tried to repair using disk utility? Does the container or volume appear in Disk Utility?
3) What disk format are you using? e.g. APFS, HFS+, NTFS, ExFat....