Many "generic" flash makers have units that are supposed to be compatible with the Canon RT radio system. Most of them include "RT" in the model number of the units they offer that they claim are compatible. Most of them are, for the most part, compatible with OEM Canon RT devices. Where it gets a little bit messy is when one tries to get two different generic "RT" flashes from different makers to work together. That's when issues seem to start cropping up more frequently.

Yongnuo is probably the most well-known Brand that makes generic RT flashes. Not all of their flashes use the RT protocol. In fact, most of their flashes do not. But those that do have an "RT" in the model number, such as the YN600EX-RT II. In the Yongnuo naming convention, the EX means the flash is TTL capable. The RT means it uses the Canon RT radio protocol. Most of Yongnuo's TTL flashes are also capable of HSS, second curtain sync, Multi flash, etc.

If all you're going to use are speedlights, then RT is not a bad way to go. But if you ever want to mix speedlights with more powerful monolights, either battery powered portable ones or mains powered studio lights, you will be limited to being able to tell those flashes to "fire" by plugging an RT receiver unit into the wired trigger port of the monolight. To change power or other settings, you'll need to do it directly on the control panel of the flash. You'll also almost certainly be limited to manual power control with no HSS, E-TTL, second curtain sync, etc.

There is another wireless system that offers compatibility with lights in their lineup all the way from low-powered, manual only compact flashes with guide numbers of less than 40 meters all the way to very powerful studio lights that output more than 1,000 watt-seconds. This is Godox, which is also sold under various trade names. Adorama in the United States, for example, sells Godox products under their private brand label 'Flashpoint'. There are also vendors in Europe that sell Godox products using a private brand label.

Using a TTL capable receiver with the Godox system allows one to have remote power control, use HSS, etc. as long as the flash is capable of doing the same thing directly attached to the camera's hot shoe.

That's something to think about before you get too deep into a speedlight only radio protocol.