ND Interchangeable Clip (IC) Filter for Canon EOS R Series Camera - STC Optics
Alpine Astronomical Baader Canon EOS Wide T-Ring DSLRT-UVIR B&H
Clip in CMOS Protector MC UV ND8 ND16 ND32 ND64 ND1000 Night Neutral Density Filter for Canon EOS R R5 R6 RP Camera Clip in|Camera Filters| - AliExpress
Kolari R Drop-in Filters for EF-EOS R Lens Adapter - Kolari Vision
NDT Fusion Auto Adapter - Canon EF Lens to L-Mount Cameras w/ Variable ND – Fotodiox, Inc. USA
Breakthrough Photography announces more than 20 drop-in filters for Canon's EF-RF adapter: Digital Photography Review