I had a similar experience on my Windows machine with a different app where the fix turned out to be to disable hardware acceleration. I’ve seen other threads where hardware acceleration doesn’t play nice with some processors and driver configs (in my case I have a 9th gen i5-9400F).
I was not able to find any hardware acceleration configuration setting for Obsidian, so my somewhat clunky (but for me acceptable) work-around was to install and run Obsidian under WSL2 instead, where the processor spiking does not reproduce.