Question about Canon RF 100-400mm f/5.6-8 IS USM

Should work. But remember that the r100 has an APS-C sensor. This is smaller than the full format, which extends the focal length by a factor of approx. 1.6.
At best, you would be better off with an RF-S 55-210mm F5-7.1 IS STM, which is smaller, lighter and cheaper.

Yes of course 👍