Not sure I understand the first two questions, so I’ll answer the 3rd : https://github.com/YunoHost-Apps/wireguard_ynh wireguard is nowadays more often recommended than OpenVPN for VPNs. You’re in luck, it’s packaged for yunohost (with a nice web ui)
Not sure what you mean exactly because I don’t know if you’re talking about vpnserver or vpnclient …
Vpnclient should work and is available as level 7 app in the catalog - no need to go through github. If the install fails then that’s a bug.
Vpnserver is not functional and not available in the app catalog. If you try to install the app using a custom repo, Yunohost at some points warns you that you probably shouldn’t do that. There’s no mention on github because … well … if somebody packages a random app on Github, we can’t force that person to put a big warning saying it’s broken … it’s just that you ain’t really supposed to install random apps from Github in the first place
Beware though that it’s still flagged as “in progress” and not in the official app catalog either. Technical reason is that it depends on the Kernel 5.x so it’s a bit touchy that installing this app would upgrade your kernel to a new major version :s