It used to be better, features like hidding owned games, search game by releaste date and many other filters have been removed for no reason. I used to buy alot from gog.com but its search engine is so awful i dont bother buying anymore from gog

Sure, the GOG website could be improved - but it doesn't bother me that much. I'm here for the DRM free games, not for the pleasant website browsing experience.

Has there ever been an option to hide owned games in store search results?

Edit: technically search by release period is still there:
https://www.gog.com/forum/general/removed_search_page_filter_workarounds