Canon EOS R5 Mark II Advanced User's Manual page 290

Caution
In some cases, this may not provide sufficient stabilization for certain lenses.
Note
For details on image stabilization for movie recording, see
Focal Length
Image stabilization based on your specified lens focal length is possible by setting the focal
length when using lenses that do not support lens communication.
1.
Select [Focal length].
2.
Set the focal length.
Turn the < > dial to select the digit of the focal length.
Press < > to display [ ].
Set the desired number, then press < >. (Returns to [
290
Movie Digital IS.
].)