Well, it looks like the issue WASN’T with Tahoe 26.3. I reloaded my laptop with MacOS Sequoia…and the same thing happened.

I tried reformatting the drive in the MacOS Extended format. Not only did that not fix the issue, the iMac stopped seeing the drive.

I had to reformat the drive on a Windows PC, plug it into my MacBook, and then refomat it one more time, back to APFS. The drive is mounting again and I have my photos on it to edit.

Looks like MacOS lives a little longer in my home.