I usually mock Nikon when they say these sorts of things, so I guess I’ll eat crow here.
Canon Japan has said that preorder numbers for both the Canon EOS R5 and Canon EOS R6 and some accessories have exceeded expectations and supply may be affected.
From Canon Japan (Google Translated)
We have received orders for the following products announced on July 9, 2020, that exceeded expectations, and it may take some time before the products are delivered.
[Applicable Products] EOS R5/EOS R6/Battery Grip BG-R10/Extender RF1.4x/Extender RF2x
We would like to thank you for all...