syspolicyd producing huge amount of read on disk
Same Macbook Pro 16 macOS 10.15.4 here.

That process verifies 3rd party software. When you open certain apps that process reads (and a lot, if the app is big). It happens to me for example when I open Photoshop 2020, it reads about 1GB.

You say you never turn it off? How much have your laptop been running? If you never power off your computer that read usage stats are not going to be wiped, so they will just keep growing, hence the huge number. If you poweroff so it starts from zero, how much syspolicyd reads in a 24h timespan?