Route Nextcloud app through OpenVPN

I have installed nextclould server with terabyte storage , but I have put behind a vpn instead of expossing it on http 80 or 443. I want to know does nextcloud ios or android app has ability to initiate openvpn cnnection so user odes not have to go to openvpn app to connect and start vpn the use nextcloud.

Nextcloud version : 17
Operating system and version : Ubuntu 18.04
Apache or nginx version : Apache 2.91
PHP version (eg, 7.1): 7.2

You will have to access Nextcloud traffic through the VPN on iOS and Android. No idea on setup process for that, but you will want to figure it out through OpenVPN documentation or other help groups.

I have openvpn working, the only thing is I have to open vpn app and sign in , the idea behind what I am asking is like some browser has option to click and vpn starts while you are browsing in their browser.

Afaik you always have to establish a vpn connection first before you can use any application on the mentioned oses. A vpn connection on Android is more flexible, because you can define e.g. the dns server or domain suffix you want to use on a per connection base, which is impossibleon iOS.