In 2024, Apple announced that as of September, it would only allow gambling apps native to iOS to be hosted in its App Store. This change was due to the fact that many gambling apps were 'container' apps, as they essentially repackaged their websites into apps, which was easier for developers to maintain.
Now, Apple does allow gambling apps on their app store as it stands, so people are able to download and play them on their iOS-based devices such as iPhones and iPads. The app developers and gambling operators do have to follow a strict set of rules to be able to get their app out to the masses though.
Games like Overwatch, Fortnite, Call of Duty, and so on require online servers to play generally, although in the case of Call of Duty, you may be able to play its offline singleplayer campaign mode even without online services active.