Japanese site Mynavi has an interview with the R1 development team. One of the topics is: “What are the criteria for a Canon flagship camera?” and it has an explanation about the name R1 (and the hyphen

).
Google translated
link.
Oh, why couldn't this have been available a month or so ago!
A short translated extract:
"
What are the criteria for a Canon flagship camera?
...
When the EOS R3 was announced, it was clearly stated that "Canon's standards do not warrant the name '1'." So what was the decisive factor that made the EOS R1 meet the standards, but not the EOS R3? The 1 series is often said to be "highly reliable," but that alone lacks specificity. There is a possibility that people will misunderstand, "Is the EOS R3 prone to breakage?" or "Is the EOS R3 vulnerable to rain?" In my experience using the EOS R3 for three years, this has not been the case. Regarding water resistance, I have heard that the EOS R3 had "water resistance to the '1' standard." If there is still a difference with the EOS R1, please tell me specifically what that difference is.
Nonomura : I think there are three major evolutions from the EOS R3 to the EOS R1.
The first is the overwhelming evolution of the AF, which I mentioned earlier. The remaining weak spots in the EOS R3 have been completely overcome, achieving AF performance worthy of a flagship model.
The second is that it is equipped with the best viewfinder in EOS history. It is the largest, brightest, and easiest to see viewfinder to date. In terms of specs, it has 9.44 million dots, a magnification of about 0.9x, and is about three times brighter than the EOS R3.
Thirdly, the readout speed of the CMOS sensor has been improved, enabling delay-free, blackout-free shooting and a significant reduction in rolling shutter distortion. I'm sure there are some people who are hesitant to switch from the EOS-1D X Mark III to a mirrorless camera because they are particular about the ease of viewing through the optical viewfinder, but I feel that the camera now has performance that I can proudly recommend.
Mr. Arakawa: Actually, we couldn't say that the R3 surpassed the EOS-1D X Mark III in terms of shutter speed or viewfinder. That's why we couldn't use the "1" in the name.
Why was the model name "EOS R1"?
- I'd also like to ask about the naming. Why did you choose the name "EOS R1"?
Nonomura : Originally, the EOS-1 series of SLR cameras had a hyphen between "EOS" and the "1". This was to prevent the number "1" from being mistaken for the lowercase letter "L" or the capital letter "I". However, since the EOS R series has the letter "R" after "EOS", we decided that the "1" would be correctly recognized even without the hyphen. As a result, we decided on the name "EOS R1" to be consistent with other models in the EOS R series.
--I expected it to be the "EOS-1R." The EOS-1 is a name that has been passed down for many years, and it was a name that was carried over even when it changed from film to digital, so I thought that would not change.
Nonomura-san: To add a little more detail, the first camera to use the "hyphen" + "1" name was the "F-1" released in 1971. The F-1 was the first professional model camera, so EOS cameras followed suit and were named "EOS-1". That trend continued all the way up to the EOS-1D X Mark III.
"