Overheat on these cameras is a difficult topic because it depends on how you use your gear. I don't have an R6, I own an R5. I can explain what I have on my R5. That could guide you in studying your R6.
I mainly use the 8K, unless I need 60fps, 120fps or crop mode.
I bought a Ninja because I thought it would be giving me a better chance, but having one more device to worry about pushed me to give up.
The Ninja itself overheat and needs a battery and its hdmi port gets loose when hot. I have to use a rubber band to keep it. As a result, I decided to give up.
On the R5, 4K regular and crop modes don't overheat. 4K60p regular doesn't overheat *. I put a star because it gives me always 29.95 time recording and since I use a ventilator (described below), I never saw that overheat sign, so I am not sure if it overheats or not. 4k60p crop overheats. 4K30 fine overheats and my favorite 8k30p overheats.
I use a ventilator in between shots. I have it turned on 10m away lying on a table and as soon as I stop shooting for a moment, even 30sec, I put the camera on top of it without removing or opening anything. I just put it on top of the ventilator. So far, I haven't had issue.
I do the same thing even when shooting using the Ninja. I simply put the camera on the ventilator every 30min or so, unless I shoot a 2h interview (just once so far) which I entirely shot in crop mode.
The ventilator I am using is below.
Honeywell HTF090BC Turbo-On-The-Go Portable Folding Fan, Black, with USB, Battery, or Electric Powered : Amazon.ca: Home
www.amazon.ca
Study it yourself to see if that can fit your shooting style.