The current PSE2021 only supports ACR 12.3 whereas your R5 requires 12.4.
Nobody know when and if PSE2021 will be updated.
So, you can download the free Adobe DNGconverter mentionned in that faq. That standalone software (not a plugin) will batch convert a whole folder of your raws to the DNG raw format that even older PSE versions can read and edit. An additional batch step, but free and with the same quality.
Or you can use the Canon software bundled with your camera and convert to tiff format to edit in the PSE normal editor.