Steam Tradingcards of games which aren't anymore on Steam

Even if they are not marketable you can still craft badges from them and you can trade them. Since they are "rare" because games are not available in Steam Store they can be sold for good amount of gems.

Pressure Booster were not expensive in the past. The boosters should have not much worth right now too (i think around 6-10 cents).
Maybe you found anyone that need that ones and is willing to pay a bit but i am sure you don't get much for them.
I think, open them, make a badge, trade the rest away against cards you need, is a good strategy

can we make a topic where could exchange those cards with posted trade links, I think it is fair to trade those 1:1 cross-game when involved games has same number of cards.

You can also trade your non marketable cards for other non marketable cards with this bot:
https://steamcommunity.com/tradeoffer/new/?partner=350991682&token=l2wZSxL5
It accepts as many 1:1 non marketable trades and helps others by making the non marketable space more liquid.

People aren't willing to pay much for those. If you're interested in crafting the badges, you can unpack the boosters and try to complete your sets from trading. (Using SteamTradeMatcher is usually a good starting point)

If you're not interested in them, and don't want to bother with trading, you can just convert them all into gems. It won't give you much but it's better than nothing.

i have two booster packs https://steamcommunity.com/id/adam_zombie/inventory/ (Torch Cave & Barclay). if anyone wants them, i have no use for them. just contact me on steam, i do not want anything in return.

Well, they're worth less than cheapest marketable sets on the market, so I wouldn't expect much if I were you. Those booster packs with help of STM are excellent source of free levels though, as you literally do not lose anything and if you craft during sale then the summer/winter card that drops will be actually marketable, so you even gain stuff out of crafting them.

If it annoys you then you can always donate them to some STM trade bot in order to help other people match them, although I see no reason why you wouldn't want to keep them, wait for eventual booster pack and finish the set. It's not like those cards take some precious space or anything. You could also find 1:1 cross-set unmarketable trade bots and just dump leftovers from 3-4 games into one full set and craft that one instead - sounds like a good idea, and wouldn't take that much time if you add all unmarketable booster packs together.