The launcher has had an issue since at least 2016 where it will consume nearly a full cores worth of CPU power if you leave it open to the Unreal Library tab. It was never fixed, to this day the launcher pulls high power on the library tab for no apparent reason.
When I used to run on a 6700k I could always tell when I accidentally left the launcher open because my CPU fan would spin up to max speed to remind me.
The launcher frankly seems to be falling into disrepair, the Unreal marketplace has been completely unusable from within the launcher for me for over a year, the main page loads but nothing happens when clicking on anything…
I can only hope a major update is coming in the future.