There are some days since when I noted a single CPU core of my system is working basically at 100% of its capacity all the time on Ubuntu (first at 18.04, but I updated to 20.04 LTS and the problem persisted). I inspected the system with htop and disabled some processes I suspected were causing the problem (like a task called 'baloo_file'), but it didn't work. I also tried unsuccessfully some things which are described here, like to install a different desktop manager (gdm3 instead of lightdm) and to install a different desktop environment (lubuntu).
I think it's being caused by some mysterious process on the system, but I have no idea which one. And I'm confident it is only on Ubuntu, since I checked it on Windows, and there things are fine. Ideas?
Here are some printscreens of htop and system's monitor to serve as evidence of the problem:
