OpenVPN is simple, but we make it way more difficult than it needs to be lol.
I was there too once with OpenVPN...tried to do all this research to find directions and got to the point I said screw it and just enabled it and kinda of followed what it was asking and it worked.
Just go to OpenVPN and enable it and see what it says - probably asks you to create a user/PW,
DDNS name, encryption method, and create certificate. Then copy and paste that certificate on your mobile device. Then install the OpenVPN app and select the certificate and then connect and you are on your home network.
It really is simpler than our minds make it out to be.
A big mistake people make is installing OpenVPN on their computer and trying to host it there, yet they are trying to follow the steps on enabling it on a router and screw it all up. Only install it on the computer to host if your router does not have it built-in.
This is for an Asus router, but the steps are kinda the same.
OpenVPN on a Asus router
Or go with ZeroTier