The only place I've found this mentioned is
this post where it says to just choose the "main" console.
Most games on multiple platforms are categorised under PC / Computer, but what if the game wasn't on PC. What would be the main console then?
Does release date factor into this? For example,
Gabbuchi is available on PC, Nintendo Switch, and PlayStation 4. But it was first released on
Switch (2019/01/31) almost 6 months before it came to
PC +
PS4 (2019/07/18). Would this make Nintendo Switch the main console or would it still be PC / Computer?
It depends on what version of the game is ripped from. Using your example, if someone ripped the Switch version then it would be on the Switch or PC for PC.
In all honesty, there isn't really a main version especially after the 5th generation where the PS2/Gamecube/Xbox had standardized ports and the differences are getting narrower each generation. While it is true that many games do have a lead system that they had used to develop the game then get ported in terms of multi-platform games (during the 7th generation, a majority of games had used the 360 then get ported to the PS3 however some games such as Castlevania: Lords of Shadow had said upfront that the lead console was the PS3) or developed on PC to begin with, a lot of the time we just don't know. Some games have enhanced ports (remasters) later down the line or downgrades to fit in terms of disc/cartridge space/limitations of the console. Games that get heavily ported such as Resident Evil 4 and GTA V or have it released on 5 different systems like right now (e.g. PS4/PS5/Xbox One/Xbox Series/PC, possibly Switch too), the main system really does blur. Not using the examples of heavily re-released games such as Sonic 1 or Super Mario Bros. as it is emulation of their original Mega Drive and NES versions in most cases, Sonic does have the Taxman ports though.
People sometimes rip the PC version because it is the easiest access (PS4 and Switch games are a lot harder to rip from by comparison and require extra tools or on the verge of piracy obtaining the files, PS4 emulation is also at its infancy) and may have higher resolution assets compared to other versions.
Besides what Yawackhary's already covered there, yeah, even if it creates a bit of redundancy in the process, the best case scenario is to just make a section for the console it's ripped from unless you're absolutely sure that the different console versions are identical to one another (perfect example here being Sonic Mania, where PC/PS4/Switch are practically 1:1). Sometimes even when things are seemingly identical, there may be differences in the graphics specifically based on the system in question (Switch having lower-resolution textures, versions having minor differences due to compression artifacting, et cetera).