SanDisk Extreme Portable SSD External Drive 1TB not recognized?

[gryphonent]

I've been using SuperDuper since, gosh, version 1 many decades ago. Didn't write in for many many years as everything (and I mean EVERYTHING) was smooth sailing.

Now, with Big Sur 11.1 running on my iMac Desktop (built late 2019), I initially was unable to backup at all and downloaded the recent update to version 3.3.1 (v121).

The strange thing is that my external SanDisk Extreme Portable SSD 1TB suddenly doesn't show up as the destination drive despite booting up properly. I used this drive for the last, say, 2 years, for backups without a hitch. But now I only see the old non-SSD drives showing as a potential destination volume.

Is this a bug or do I have to get a non-SSD drive for backups with Big Sur/SuperDuper 3.3.1?

Take care,
Jurgen