I have found that in Linux, "nrfutil toolchain-manager launch --shell" is starting a process that uses almost 20% of the CPU according to the top utility. I have found this directly on a Ubuntu machine and also with Windows Subsystem for Linux. I may be running 24.04-1 but I am guessing it will be the same for 22.04-1.
I don't know why it should use any resources if it just exports environment variables. In fact, I tried to tease out most of the environment variables added/modified by nrfutil...--shell and run a simple script that exports the same variables into a basic bash shell. This seems to allow me to build and I don't see anything gobbling up CPU. But I'd rather run nrfutil...--shell rather than my hack script--minus wasting CPU.
Burt