Answer: Maybe. The registration distance of the EF-M mount is shorter than that of the RF mount. This would mean that with the typical glassless adapter design, adapted EF-M lenses would lose infinity focus and only be focussable to close distances. Adapters with glass can have advantages – using glass elements, a teleconverter could be made that increases the imaging circle of the M glass to fill the EOS R full frame imaging circle.
However, let’s explore the other remaining possibility. The throat diameter of the RF mount is also considerably larger (by 7mm), which means that in theory, an EF-M adapter could be placed 2mm deep inside the RF mount to compensate for the difference in registration distance. But what of the width of the bayonet mount “brim”? As you might expect having eyeballed the numbers, only 3.5mm are left either side for a bayonet brim and electronic wiring, which isn’t near enough for the EF-M mount – and the lenses do use the full width of the brim!
Now, Canon seems to enjoy playing around with different adapters for EF glass on RF-mount cameras, having released three or four different models so far. So it would be silly of me to deny the possibility of such an EF-M to RF teleconverter coming to market (presumably with depth of field as it would be on APS-C and the usual 1-stop dilution of light). However, it seems the market share of the EOS M cameras is quite modest, and the number of lenses even more so, with perhaps fewer than 15 from any brand providing autofocus, and only eight from Canon. So the question really becomes, will Canon risk alienating its faithful? That presumably depends on how determined they would be to change brands if left with a dead system.
And while the similar cancellations of the Nikon 1 and Pentax Q systems do not seem to have had a major impact, those were clearly toy systems from the beginning, so users presumably had much less of an expectation that their system would grow into something serious – although Nikon certainly tried!
One hint might be in the fact that Canon chose 20mm rather than 18mm or 16mm as the registration distance – ironically, Nikon put its peg at 16mm, which would physically allow an EF-M to Z adapter. But will Nikon brave a lawsuit to rescue a few marooned Canon users? As always, time will tell.
Update 2021/01/02: If you’d like to know what your EF-M lenses will turn into with a 1.4x teleconverter, check this out.
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breakfastographer 
trying to put as EF-M lens (which is designed for an APS sensor) on a RF mount body doesn’t make much sense anyway.
It would be far more interesting to do the other way round : be able to adapt an RF lens to an EF-M body.
In that case the flange depth difference allows 2mm thickness adapter, and the diameter difference is not a problem. … could even get some speedboosting witnh thin optics…
The idea of cropping to a smaller format was established years ago with the marketing of the Sony RX1 if not earlier, and has become established practice when mounting APS-C lenses on full frame cameras. Typically, an automatic compatibility mode is provided that recognises the lens and chooses the appropriate crop. On a DLSR, you may see a dark circle in the viewfinder, and probably a crop marker to help you compose your shot – for example on the Pentax K-1. On a mirrorless camera, the experience can be even more seamless as the cropped image can at least theoretically simply be scaled up in the EVF.