This seems to be a stupid bug that I encountered with some other games as well. Kiana, that is the reason why I made my post here some months ago. The problem still exists, the itch app says "not available".
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Would appreciate a feature that let's you "own" free games (so you can see them in your collection) and when they become paid versions, you could maybe grey them out and be like "If you want to continue owning this game, please pay its price to support the developer."