The command I've seen from How do I disable mouse acceleration AND adjust tracking speed in High Sierra?
defaults write .GlobalPreferences com.apple.mouse.scaling -1
Doesn't change the mouse behaviour at all.
I don't know where to download SteelSeries exact mouse anymore (nor if it works). Ideally a solution should exist that doesn't use third party software.
I have a logitech G203, Macbook Pro 15", macOS Catalina 10.15.2.