There are a bunch of links on the relevant OSMF page (including contact addresses) that may help. They’ll know what action would be appropriate here.
The merchandise just says “OSM.shop”. That isn’t a trademark of the OpenStreetMap Foundation, and nor is “OSM” - that can equally apply to Online Soccer Manager or the Orange Survival Militia or Orangutans Supporting Musk. The OSMF trademark policy asserts ownership of “the abbreviations when used in the OpenStreetMap or geodata context”, which these don’t appear to be.
If you would at least browse more first, “About” claims to be “Open Source Merchandise”. That’s labeled on Twitter.
“OS” can stand for Ordnance Survey here, or Operating System. There was another random one by Microsoft. Open Service Mesh - Wikipedia
It’s entirely possible someone made this website for learning purpose. For any seriousness, the “OSM.shop LLC” needs to be looked up, as far as whether the company can be registered easily. I got blocked by the business list showing it.