Mac Mini not recognizing Samsung NVME external anymore

First mistake was installing and using the Samsung software.

1) Move the data from the SSD to another drive.

2) Completely uninstall the Samsung software from your Mac.

3) Erase the Samsung SSD using GUID Partition Map and APFS Format.

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

4) Then copy the data back to the Samsung SSD.

Pritch wrote:

...Once the Samsung software was installed.....

Follow the manufacturer instructions and completely un-install their software. These days there is absolutely no need to install a special software from a drive manufacturer and it generally creates more problems than it solves.

Second, verify that the Samsung EVO Plus drive is compatible with the enclosure and with your Mac. Not all combinations of DIY enclosures and NVMe drives play well with any given computer make and model, especially the higher performance enclosures like Thunderbolt or USB4.

Third Samsung EVO Plus line of SSDs have had some history of being problematic with Macs in high performance DIY enclosures while the Samsung Pro series have been bulletproof.

For what its worth, I have a 1M2 enclosure that I purchased prepackaged with a 1TB OWC Aura Ultra IV and it has been running flawlessly and is just as fast as the internal SSD on my M4 MacBook Air. The OWC line of SSDs have been nearly flawless performers and many in the community will attest to.