Canon USA: https://www.usa.canon.com/support/p/eos-r3#idReference=software-drivers
From the release notes:
Edit: Craig has a news article here: https://www.canonrumors.com/canon-eos-r3-firmware-v1-9-0-now-available/
but it doesn't show up and it seems I can't reply to it as I'm "not logged...
Just a short info for users of EF version of the current 600mm f/4 (Mk III in EF mount): if you want to update the firmware of that lens (currently 1.1.3), better use a current R system camera + adapter. Updating worked flawlessly with my R7.
Problem with a 5D4, and this may happen with other...