I'm having issues downloading the firmware for my Canon R5C. When I go to download from this page it just links me back to the main camera page which doesn't include any links to download. Perhaps there is something wrong with Canon's website tonight...
For what it is worth CanonUSA did confirm that the R5C is compatible (in Photo mode) in the comment section of the EL-5 Youtube video:https://www.youtube.com/watch?v=ZOrFhFtU_p0