Wow, I finally found the SOLUTION!!! The same .ovpn config file works now for both Windows and Android!
I now totally understand why you couldn't help me
Both OpenVPN Connect for Android and OpenVPN from Arne Schwabe apparently didn't find any data in my .ovpn file. When I open my file in Windows with Notepad, I can perfectly see normal text in the .ovpn file. However, when I send the file to my phone via e-mail to my own e-mail address and I open the .ovpn file with a simple text editor, the file is blank! Of course the apps cannot detect any configurations from an unreadable file and give errors like 'there is no remote chosen' or 'no CA certificate is present'.
I also did a separate test: I created a random .txt file on Windows with Notepad, then I sent it to my own e-mail and tried to open it with a texteditor. Now the file appeared not empty, but only some unreadable strange symbols were visible.
SOLUTION:
The problem is a very very very specific bug! When you send a simple text file like .txt or .ovpn with a mail address that is configured with IMAP in Microsoft Outlook 2019 to another (or your own) e-mail address that can be IMAP configured on the Gmail app on your Android phone, then the .txt attachment becomes corrupted upon opening. It becomes also unreadable in Windows when I would bring the file back to my Windows PC by transferring it via USB to my PC. So the file is permanantly corrupted.
When you would open the same received mail with another IMAP configured Android mail app, the file is not corrupted.
When the email sender uses the webmail interface of the email-provider instead of IMAP in Outlook, then there is also no problem when the receiver opens the attachment in the IMAP configured Android Gmail app.
When you use non-IMAP configured e-mail addresses as sender OR as receiver, there is also no problem.
In fact this bug should be send to both Google and Microsoft. Do you have connections?
I would never have encountered the problem if I would have just used a USB connection to transfer the file to my phone.
I am so happy my Open VPN finally works on Android!

All this waste of time just because of a stupid mail bug that has nothing to do with OpenVPN
