There are unlimited digital copies...it was just in sale in fact, 50% off ($30 usd) probably go back on sale in a couple weeks.

I have never found it so hard to find a game from a current gen, no matter how old is the game

Here ya go, looks like Gamestop has some used copies: $18.99 usd: https://www.gamestop.com/video-games/playstation-4/products/final-fantasy-vii-remake---playstation-4/211484.html

I also see it new on Amazon for $30: https://www.amazon.com/FINAL-FANTASY-VII-REMAKE-playstation-4/dp/B07SV4S75P