The Bank ID app, that is standard in my country unfortunately depends on Google Play Services. It is practically impossible to do anything like paying bills or buying stuff without it. Hence I wonder if it is possible to install said abommination when installing /e/:s operating system (probably on a Samsung Galaxy S3 i9300).
Regain your privacy! Adopt /e/ the unGoogled mobile OS and online services
No, it’s not possible to install the genuine Google services on /e/OS, because /e/OS currently has microG integrated in a non-removable way, which tries its best to mimic those Google services.
And /e/OS includes further degoogling changes, which possibly could interfere with operating the genuine Google services reliably anyway.
That being said, with the help of the integrated microG your banking App might even work on /e/OS, at least for a while, but there are no guarantees … [LIST] Banking Apps on /e/OS
If you really, really need your banking App (or any Google-dependent App for that matter), in Custom ROM territory you would be better off using LineageOS in connection with the genuine Google services (installed e.g. via Open GApps) and Google’s registration of devices running uncertified Android OSes for the legitimate use of Google services at https://www.google.com/android/uncertified.
Does your bank not work via the web?
does MagiskHide help ?
as it hide the android customisation (no verified-boot) to my personal bank-app ?
Sadly, signing in via the web also requires the bankid app.
I am not familiar with MagiskHide. Could you give a brief explanation?
which bank app is that ?
@udengoogle It’s not a banking app, its an identification app with a somewhat misleading name. Also, which bank I use is a piece of information that could be used to identify me or possibly steal my identity. I wish to remain as anonymous as possible. I hope you don’t mind me not sharing in a public forum like this!
Please forgive my bad english,
In short :
Magisk app modify the system /boot.
Magisk Manager can allow the apps you choose, to get the root permission.
MagiskHide module can hide to some apps you choose, that the system is not a stock guewine brand vendor one (verified-boot), and that root is allowable/available
Success! microg works fine for me. 
What have you doing for that ?
I installed /e/OS on a galaxy S5 and then installed the Bank ID app and it works as expected. Not a problem so far. Seems microg does the job of replacing Google Play Services well for my usecase.
I have been using a de-googled Fairphone 4 since more than a year now.
First I was using /e/OS (up till version 1.8.1). Most apps, including banking apps, worked flawlessly.
Then I moved to LineageOS (20.0, without any google layer) and several apps did not work properly anymore (including banking apps but also other apps such as Tripadvisor or theGuardian).
Thanks to @AnotherElk 's post I understand why.
just use system app uninstaller to remove fake store and microg
also remove app store just in case
root and twrp needed for it…
flash opengapps
enjoy lol
deggogle can’t be force because google is creator of android
lolol