So I've had the reverse issue. With hardware encoding on and external monitors plugged into my intel macbook, everything would overheat and I would get kernel throttling of everything.
The external monitors cause the GPU to draw more power, but I'm not sure why that combined with hardware encoding in OBS caused issues. When I switched to software encoding the cpu was a bit higher but everything was fine.
Apparently this is related to VRM overheating and people have workarounds posted on reddit, but it seem like switching to software encoding made it go away for me.
https://www.reddit.com/r/macbookpro/comments/gs6bal/2019_mbp...