I am not aware of any extension tubes for the RF mount, only the EF mount.
I do not recommend using them with RF-EF mount adapter. Canon has made extension tubes for the EF mount. So far, Canon has not released any for the RF mount, AFAIK.
The adapter itself is just a tube, so from an optical point of view, it makes no difference.
There are macro rings for RF mount, on ebay, from who knows what manufacturer. The may be fine, but like Wadizzle says, I would be more inclined to trust tried-and-tested EF mount tubes, which have been around long enough for plenty of people to have reviewed them. Macro rings don't have to do a lot, basically just the mechanics and straight-through wiring for the electronic connection. But cheapo third-party junk can always find some way to screw up.
But of course EF tubes will only ever work with EF lenses. That may be a factor. RF tubes would work with anything you can put on the camera.
That's why one end of the Lens Adapter is larger than the other. The adapter has no effect on the MFD (minimum focusing distance) and the distance should remain the same as it would on a DSLR with an APS-C sensor.
I try to distinguish between lens adapters and mount adapters. A lens adapter is mounted on the lens, where it stays. A mount adapter is mounted on the camera, where it stays mounted to the camera.
I categorize extension tubes as mount adapters, which means they mount to the camera and stay there. The EF-RF mount adapters for the R Series bodies are needed for adapting EF mount lenses.
Adding one extension tube to a body is fine. When you begin stacking them is when you can start running into problems with budget priced adapters. The stack of extension tubes can begin to become a little wobbly. Not a whole lot wobbly, but more than enough to have an impact on focusing a macro distances and narrow DOF.
I foresee this “wobble” problem only becoming worse when there is already a mount adapter on the camera body.
In answer to the original question, I don't know why you couldn't use them and don't think it matters very much where you put the extension tubes.... between the lens and the lens adapter... or between the lens adapter and the camera body. Either way the result is the same... the lens is moved farther from the sensor and will focus close, rendering higher magnification. Since an EF 100mm Macro can already do 1:1 on it's own, adding extensions will make the lens able to do higher than life size magnification.
However... There simply aren't a lot of extension tubes available for RF-mount. Canon doesn't make any yet. Several 3rd party manufacturers have stepped up with somewhat limited choices or individual tubes: https://www.bhphotovideo.com/c/products/Extension-Tubes/ci/276/N/4077634539?filters=fct_camera-body-...
In contrast, there are many that have been or are still being made for the EF mount... both by Canon themselves and a number of third party manufacturers. https://www.bhphotovideo.com/c/products/Extension-Tubes/ci/276/N/4077634539?filters=fct_camera-body-... If you wanted you also could probably find a lot of them available used (not much to wear out, so I would consider used tubes so long as they are a quality brand like Canon or Kenko).
Just be sure to get the type that has the electronic contacts... NOT the really cheap ones without any electronic support. That way you will be able to set the lens aperture, and if you wish use AF and IS, if the lens has it. I use several of the Canon tubes (two 12mm and a 25mm) and the Kenko set (12, 20 and 36mm) pretty much interchangeably.