The DHL App works without problems, even on the newer Packstation that has no screen and uses Bluetooth alone.
I don't know if Sparkasse NFC works (I guess it will as long as the app works), but if not, in Germany you can use PayPal NFC via their app and you could connect your Sparkasse Bankkonto with PayPal and use that for payments in supermarkets.
I switched from iOS to Graphene and at first i made the mistake to make to many profiles, but it turned out it is not useful if you need Google Play Services dependent Apps daily.
I just use one profile (the owner profile) together with Play Store and Services. It's easier that way to use messengers, banking apps and also RCS with Google Messages.
You still can hide personal things by opening a private space in that user/owner profile. But it is not really necessary.
Doing everything from the owner profile will be the best experience when coming from iOS, because you will make sacrifices in regards of convenience. iOS is offering out of the box solutions that GrapheneOS doesn't offer.
That starts with setting up email accounts (an Android related problem). In iOS you just put all email providers in the mail app and it works. On Android you either need to install one app per Mail Provider or use a third party app like DAVx. You will need the latter for synching Calendars as well (together with apps like aCalendar etc. ) and /or use the calendar specific app (Google Calendar, Yahoo Calendar etc.
For Passwords you need an app. I would suggest Proton Pass, you can integrate your iOS keychain passwords into it (they explain on their website how, you need at least for one time a desktop computer).
The backup solution on iOS is much easier. Oh the other hand, copying Photos and other data is much easier on Android, as it just needs a cable/USB stick/portable SSD etc.
But they have it on the roadmap to provide a better integrated backup solution coming in the future.