Sure. You should always try to follow the conventions of the platform you're on.
A great example of what not to do is Microsoft Word for Mac, where many of the keyboard shortcuts follow Windows conventions. Seems fine for users of one platform, disorienting and annoying on the other.
I don't use both Android and iOS simultaneously as a primary device, so I don't have any hard data on density or frequency of notifications, but you might find iOS users are getting fewer notifications on their devices and therefore you want your app to show fewer messages.
Or, as Dominik pointed out, different platforms have different capabilities. For example, if a handy feature of your app is to take some action directly from a notification, but said feature can only be implemented on one platform, then you may find that the notifications are less useful (or even useless) on the platform that doesn't support the direct action.
If an alternate method would be supported, such as SMS/Facebook, I would make it available to all users. With a PWA you might find many edge cases and reasons users don't want or can't use traditional notifications.