Notification problems and tips for a newbie from Android

It’s nice to be here - I have an iPhone 13 mini as my first non android since smartphones existed.

I’m still using Google Calendar but the reminders are only staying in notification centre for a couple of hours then disappear. Any ideas why this could be? I have them as persistent.

The other question - are there any top recommendations for a total newbie? So far I have kept Google maps, calendar and Chrome browser (for passwords). The rest are whatever was on the phone.

Thank you!