In particularly Apple is not supporting or poorly supporting features associated with "Progressive Web Applications" on mobile to prevent PWA's from competing with the app store on iOS.
Sidenote: I love Apple products, but to be honest Apple is not the best at making software. Recently, the quality has declined too. Their great applications are a few niche professional apps not designed for the average user. They have also gotten a lot slower at releasing updates.
I am a software dev at work and we had a time period where our product (React-based SPA) wasn't working on mobile Safari because of 3rd party cookie issues -- in the long term though the world was going that way and once we changed our cookies Safari works just fine.