It's the plastic diffuser... I have no idea what that thing is called. The clear plastic piece that pulls out of the end to spread a wider coverage. It's out, possibly just a tiny bit. Pull it all the way out and put it in firmly. Happens on occasion.
I believe the zoom only goes down to 24mm, the diffuser does something wide like 14mm and will flash that icon to let you know its out.
Note that you do need to use that diffusion panel with the wide end of your 16-35mm... any focal length 23mm or wider... but not with the 24-35mm range of that zoom or with your 100mm macro lens.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
04/20/2023: New firmware version 1.4.1 is available for EOS R3
03/30/2023: New firmware updates are available.
2/07/2023: New product announcements!EOS R8 EOS R50RF-S55-210mm F5-7.1 IS STMRF24-50mm F4.5-6.3 IS STMRF15-30mm F4.5-6.3 IS STM