The Steam version is a nice way to sell open source software. It has an additional interface designed for tablets, which is open source, but the free builds from krita.org don't include it.
The current steam version is same as the free version, with steam version you get automatic update, The tablet version is Krita Gemini, i think it is the older version, i don't know if it is still on steam, as recently steam version was updated
It's also on the Windows/Microsoft Store which means I get auto-updates.