I’m using OpenVPN Connect on an iPad and it works flawlessly for me. Also with multiple VPNs. Agreed, it doesn’t look very nice, but if all’s well you only see the app when connecting and disconnecting. It’s the “official” OpenVPN app too.
I don’t think there are any alternatives to OpenVPN Connect if you want to use OpenVPN. This App has (or used to have) special permissions to offer/integrate OpenVPN in iOS.
The interface of the App is indeed ancient (and “ugly”), but I (almost) never see it. Using profiles you can enable/disable your VPN from the iOS Settings App (and even let it auto connect/disconnect - “On Demand”).
I think they were working on a refresh of the GUI for version 2.0, but they haven’t released an update in quite a while. Unfortunately my setup is currently partially broken due to a bug in their latest version (I can’t use “On Demand” for ProtonVPN).