Any Idea What This Might Be?

I would agree with this. The big marker at a grave can be called a headstone and a small one like this at the other end of the grave is the foot stone

If it was a grave marker presumably it would include dates. Some sort of memorial stone is my guess. Maybe intended for use in a path or wall, or maybe just a housewarming gift meant to be used as a doorstop.
Definitely Soderholm with an umlaut. It’s a common enough name. I can’t make out the first initial.

It looked clearly like “H. Süderholm” to me, even before reading the posts in the thread (so I wasn’t influenced by them). Only the “er” gave me a little pause.

It doesn’t really look like a regular Fraktur to me. Fraktur has rounded right-hand sides of the small “o”, and the “S” is not shaped like that (although you say it looks like an “J.” It doesn’t look a “J” to me, but an “S” in a blackletter font of some type, but not bog standard Fraktur.)