Canon might soon announce a RF 20-40mm f/4 STM pancake lens for the EOS R system.
The rumor surfaced on Weibo, and not much is revealed. Here the machine translated text:
It is whispered that a Canon RF 20-40mm F4 STM full-frame mirrorless pancake lens that emphasizes portability and convenience when shooting movies is under development (generally credible). RF mount video pancake lenses have also been rumored once before, but there is no new news since then.
Guess it is entirely possible for Canon to release such a lens. Time will tell. Stay tuned.