Yes, the game is legal. However, Apple prohibits explicit adult content on the App Store, which is why you must sideload it. You are not breaking any law by installing it for personal use.
: This is the safest method. You run the game on your PC/Mac and stream the screen to your iPhone using apps like Steam Link Chrome Remote Desktop Web Browser download summertime saga ios verified
To get a download that actually works long-term, you must use a sideloading method approved by Apple’s developer framework. Yes, the game is legal