For some reason one core always used 50% more than others. What steps to investigate that?

I don't know when this started. Few months ago all cores shows same % usage.

Edited March 23, 20215 yr by Nuke

I think you might be looking for problems where there aren't any. For example, would you be any happier if all four cores were showing 10.8% usage instead? it's impossible to say as you haven't provided the information but maybe the kernel is favouring your most capable core. You need not worry about wearing it out!