For contacts, email, calendar…

The native iOS apps work well with gmail accounts. Contacts with gmail accounts have slightly reduced functionality.

Google’s own apps for mail and calendar exist and work well enough.

Bitwarden …

It works quite well with all the apps, including Safari, bank apps,food and take out apps, etc.

Vanced…

Does not work. You will have to buy a YouTube premium subscription. You can get around it by using a Safari extension such as Vinegar. Vinegar will let you play YouTube videos in the background and so on.

Apollo for Reddit is the GOAT. Don’t bother with any other Reddit client, including the official one.

Earphones and smart watches …

They will work with an iPhone. But in less than 6 months, you’ll want to switch to completely to the “ecosystem” because they “just work” with each other.

Pretty much all the other apps you see or know off work quite well.