preview/quicklook of jpg only shows generic icon, not thumbnail.

Fritz Lang1 wrote:

I've toggled Finder/View and looked in prefs, but still no thumbnail.

Is that a feature of Sequoia?

Not a feature of Sequoia. I am running v15.6 and all of my .jpg, .jpeg, and .jxl images appear in the Finder or their enlarged images via Quick Look.

What third-party tools have you recently installed, or have you changed the default opening application for these images?

I do not install any unnecessary tools into macOS and Pro Tools falls into that category by my standards.

I have two .webp images that I downloaded from the Internet and both display just fine as Finder icons and respond properly to Quick Look.