RF-mount lenses are not compatible with EF, EF-S or EF-M mount camera bodies.

Can you adapt RF lenses to EF?

RF lenses fit the camera natively – i.e. without the need for an adapter. At release, all EOS R and RP cameras are being supplied with a mount adapter – the EF-EOS R – which allows you to fit both EF and EF-S lenses to your R-series camera.

Does RF fit EF?

Thankfully, EF and EF-S mount lenses can be used on RF mount with an EF to RF adapter. They're widely available and pretty cheap. Canon's standard EF to RF adapter is only $99 and works reliably. However, RF mount lenses cannot be used on EF mount at all at the moment.