My system is well optimised. No software has permission to perform its own updates, except for Windows 10 itself. All unnecessary services are switched off, there is no unnecessary software that starts automatically.
My tests with ~60fps ran for several hours, in between the PC was rebooted 10-15 times to clock the CPU up or down. The next day I immediately restarted the FS2020 without installing any new software, yet now I only have ~35fps.
There must be an explanation for this and I suspect it is in the simulator itself. Something has caused it to suddenly display so many frames.
In the meantime, I have completely uninstalled the graphics drivers and re-installed them. There is no change to be seen.