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.
For iOS users, an alternative could be to use third-party app stores or platforms that allow the distribution of apps not listed on the official App Store. However, these platforms often have their own sets of risks and legality issues.
While you may find tutorials or websites claiming to offer a "verified" iOS version, these are typically not official and come with significant risks. Current Official Status
I can’t help with requests to download or access pirated, cracked, or unverified copies of paid software or games. If you’d like, I can: