An adapter is fine, but Canon should have designed this from the ground up for video.
Canon should have made the R5 far bigger so it could handle the heat better.
They should have included fans and a far bigger heatsink. While they were making it bigger to better handle the heat, they could have put in built in NDs to make life more convenient for the video shooter.
Oh and with a bigger body to handle the heat better, they could have also put more buttons on the body so that you could change key video settings without having to go in to the menu i.e. dedicated buttons for ISO / shutter / FPS / peaking / zebras etc.
With a bigger body they could have also then had full size HDMI and better audio input abilities e.g. dual XLRs and on-body control for the audio levels etc.
With a bigger body, they could also probably have managed to come up with a solution for swapping out lens mounts easily so YouTuber bloggers could switch between EF and PL mounts for their Vlogs.
Finally they could have had a bigger screen and also larger EVF to make working in video far easier. In fact, they probably just should have removed all the photography features and weather-sealing of the R5 because it's clearly just compromising the video side of the camera.
If only such a camera existed in Canon's range for people that want to do video....
Obvious sarcasm is obvious. LOL!
For 79.99 Canon will just swap out your doorstop R5 for a new C300 MkX with 16K 240 fps liquid helium cooled camera that chews through 8 terabytes of data in 10 seconds. The vbloggers, influencers, and Sony fanboys will still not be happy, and Sony Northrup will still give it a bad review though.