Yes gog is losing money at this time. They depend on cyberpunk sales. Right now gog has many options to close in the future because it generates losses.

The humble FAQ specifies it as ~5%, it may include fraud management as well.
That's... unexpected since I think they also folded the Gwent card game into GOG's revenue. Though perhaps development costs for Gwent are also for GOG to cover.

There are two main factors:
1) CDPR product sales are down a lot this year, particularly GWENT.
2) The PLN increased in value vs USD and since the majority of transactions are in USD, they take in less PLN.

On the plus side, external clients (i.e. non-CDPR products) have increased 22% if aggregated in USD instead of PLN (discounting the currency fluctuation). Indicating that individual game sales are fine if not better.

A quick number crunch estimating the loss if GoG were to cut their take in half, they would have lost an additional 14,317,500 PLN this year.

That mindset might still endanger the store. Suppose for some reason the profit margin of GOG may be lower than of Steam or Origin, maybe because sales volumes are lower and fixed costs are relatively higher. If now GOG increases the fee (or does not decrease the fee together with the others) then prices on GOG will be higher than elsewhere, even less people will buy here and the profit margin will be even less if the relative weight of fixed costs increases further. In the end GOG, by not cutting the rev share, could end up facing bankrupty all the same.

Steam and Origin have big financial reserves. What if they decide to undercut GOG significantly? By not doing what the rest of the industry is doing they risk lots of bad things. GOG doesn't need to have the lowest rev share of them all but it should also really avoid having the highest.

The best thing for GOG would be growth and a lower rev share may positively induce growth. However, I guess that in the case of a permanent operating loss they should rather cut expenditures instead of increasing their rev share.

Humble widgets (which is hosted on the developers own sites, not in the store) is 90/10 split. The Humble Store (I think) is 75/20 + 5 to charity (for Humble Bundles you can decide what cut to give Humble).

itch.io is also an exception, as the developers can decide themselves how large cut they want to give the store (all the way down to 0%)

If GOG makes a loss at 70/30 and other stores have cuts which are better, how can these other shops make profit then?

Humble Store or Itch.io is probably not (much) bigger, so I would expect a similar cost structure? GOG may have better support and game testing (especially of the classics) which might justify a higher cut.

But especially if itch.io would get 0%, how could they survive at all?

The widget is 95%/5%, after payment processing.

Except that "creative accounting" is mostly an urban myth. There are strict laws involving what counts where and any changes have to be made publicly and explained (which CDP has done throughout the years). Once divisions are set up, they can't be making a lot of changes. The limit to "creativity" are things like explaining how external sales revenue is up 22% if one normalizes it to the U.S. dollar. It's positive speak for the investor, but one also needs to read between the lines. They used quite the number of qualifiers there. But accounting wise, they can't just move money all over the place like that. That's just in the movies or companies engaging it intentional illegal acts.

CDPR is doing great, even with sales dropping. So the company as a whole is fine. I was pointing out that GoG just doesn't have the same margin for error. It's not a bad loss so far. They have lost less than they profited in the same period in 2017, so for the two years combined, they still have a profit. They also played around with networking and matchmaking services with GWENT which I imagine might get applied in the future to other games. Possibly a future matchmaking connection for LANs through Galaxy. I know most people here talk trash about it, but I think part of the plan was to use it in this way.