Log is not a video format -- it's a gamma curve. A video format -- like MP4 -- saves pixels, which are just numbers, in a file. The gamma curve, whether it's Rec 709 or Log or whatever, dictates what those numbers mean.
In other words, changing from Rec 709 to Log will not change the file format; it will only change how the pixels in the file are encoded. It's up to you to decode those pixels correctly in post. Generally, a video editor will assume that your pixels are encoded in Rec 709; normally you would add a LUT to your footage to correct it from Log to Rec 709. You can find the official Canon LUTs for this here: www.usa.canon.com/support/p/eos-r (look for "Canon lookup table Version 201911").
Generally you want a 3D LUT, and 65-point grid is best. So to decode Log 3 to Rec 709, for example, you would use "3dlut\65grid-3dlut\full-to-full-range\CinemaGamut_CanonLog3-to-BT709_WideDR_65_FF_Ver.2.0.cube".
Note that to get the benefit of Log, do your exposure correction BEFORE applying the LUT. For example, in Premiere Pro, under Effect Controls, I would add a Lumetri Colour effect to fix the exposure, and then add another one with the LUT BELOW it in the control panel.
Hope this helps.
