@iDeSmI Tachiyomi doesn't have an iOS release.
@Pauan NetworkInformation.type is a draft API that is not supported on iOS (or desktop, for that matter). Service Workers are supported on iOS, but not for push notifications or background sync, which is basically the entire purpose you're proposing them for. You're ultimately limited to only being able to populate the cache when the user is actively using the app. For offline support, that's not useless, as it does cover scenarios where the user has connectivity and then loses it unexpectedly (or temporarily), but doesn't cover the "user pulls their phone out to read manga while in the subway" scenario.
I still think an application shell around a progressive web app would be the best compromise: the vast majority of the work/effort would be cross-platform, and should anything happen to the app store entry (such as removal by Apple or Google), it would still work in the browser, albeit without a few features like background sync.