Windows 10 came with an application to view 3D models in obj and other formats, but it's no longer included in Windows 11. You have to download it separately now (it's still free).

Then download and install F3D instead :)

Macs mostly do it, unless it's STEP, nobody can reasonably open a STEP file, even scihub doesn't have the specification.

The OCCT library can read STEP pretty well, but there's nothing small or light about leveraging that ;-)

F3D rely on OCCT to open STEP and IGES file, just try it :)

The only other Free Software STEP reader of any competence might be the one in gCAD3d. It's written in C. But even if you can read STEP there is the problem of triangulating trimmed NURBS surfaces. I've been wanting to lift that reader and put it in Solvespace for linking parts in assembly but it's a big job and we still can't support all the types of geometry you might find in STEP.

Windows 11 shows STEP thumbnails now.

By default ?

Yes!

Yeah it’s been built into macOS natively for quite some time.

Windows powertoys can preview and thumbnail STL files.

Operating systems don’t even have software (anymore) that allows looking through multiple images in a directory.

Which operating systems are you talking about? I can do that just fine in both windows and macOS without installing anything

macOS supports viewing USD, STL, Alembic, PLY, OBJ for almost a decade now (some formats being newer).

Windows as well supports gltf in many areas.

iOS natively supports USDZ for the last 5-ish years.