For "finished" products like Gwent, its development expenditures (post release) are expenses.

It would depend. Typically you're looking at a mix of capital costs (Buildings), salary (researches, etc.), equipment, supplies/materials, travel.

Under GAAP some of those are amortized (buildings, equipment) and the rest are not, and would be a direct expense in the year they were incurred. It gets more complicated when you are purchasing things like patents or goodwill for R&D that are themselves treated as assets.

But Poland appears to use IFRS rather than GAAP, so my memory of GAAP may be missing something in what GOG is doing, plus I glommed onto this conversation late.

My guess would be "Selling Costs" as it relates to servers and expenses for a released game they are selling, namely GWENT.

Most likely Cost of Products and maybe General and Adminstrative, depending on breakdown. Ofc it can have parts show up in the Selling Costs too. Without seeing the detailed balance sheet it's impossible to tell.

R&D is kinda separate from expenses

Also GOG is doing some 'creative accounting' by somehow making 50% of GWENT development a GOG expense

There is no such thing as separate from expenses. Every expense has to show up at some point. It only depends on how it's distributed and if it's amortised long term or it's written off in a lump sum.

I meant it more of whether they treat R&D as 'capital' expenditures vs 'expenes' which are treated very differently

They are, but still on the long run will show up as "depreciation expense". But yes, they might not show up immediately, just as i wrote above.