As long as the RF extenders are not officially on the web page they will not be put into the compatibility category of any lens.It’s on the official product page on the Canon website. Click on ‘specifications’ and scroll down to ‘Extender compatibility’.
Today yes, an EF converters is not compatible with RF 70-200
The RF will be compatible, the 70-200 has dedicated space left to fit.
This will give nice setups, especially 100-280 F4 with the 1,4x should perform great.