Tamron has released a firmware update for the SP 150-600mm f/5-6.3 Di VC USD G2 to add Canon EOS R support.
A022 SP 150-600mm F/5-6.3 Di VC USD G2 Ver.2:
Enable general operations on Canon EOS R with Mount Adapter EF-EOS R by the firmware updating.
[NOTE] Canon Mount Adapter EF-EOS R is required to attach the lens to Canon EOS R.
You can download the firmware here.