Known issueFixUpdated · 4 replies on Steam
9 Kings: Card Drag Issue (Workarounds)
Short answer
Suggested fix (unconfirmed): Switch the game to full screen mode. If toggling full screen fails, try running the game in windowed mode or switching your desktop environment's window management settings.
The problem
i can't drag cards with my mouse, they just minimize and return to my hand, if i try to drag them. If i play it clever, i can play a card in the corner that overlaps with my cards, over all, the game is unplayable this way. i am on arch linux with recommended proton settings
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Source: original Steam Community discussion. Quotes are shortened; all credit goes to the posters.