I have purchased Nanopi Neo 3 which is very simular to Nanopi R2S this week and after the installation of Armbian Buster 5.4 noticed overheating. After entering Htop, I found a process completely using the processor. PID 907 is the admin login for it, PID 898 is the root login for it. The command kill -9 898 or kill -9 907 solved the problem of overheating and 100% load. The processor temperature dropped to 66 degrees Celsius.
Perhaps the next step will be the replacement of the installed cooling system with a DIY one.
I hope that my experience will help anybody else.
