Yeah, if there’s anyone who need vanilla OWRT, it’s you. You really do need full access to the OpenWrt ecosystem. GL builds an incredibly easy to use GUI but they also make some deep modifications to OpenWrt to make that happen. That’s a problem.
The fact that GL themselves are based in a hostile terrority that is the CPC some VPN technologies aren’t going to be supported… for example, if you bought your Flint v2 in Asia from, say, Alibaba, you wouldn’t have any VPN options. I wish I was kidding.
Regarding GUIs: stock OpenWrt ships with a GUI known as LuCI. It’s already on your Flint v2 (GL GUI → System → Advanced Settings; same password as GL GUI, username root ). It really is more advanced… but you’ll still have problems from the GL customizations regardless (eg: iptables firewall/routing modifications).
Can you access Youtube without interference/restrictions in Iran? I’ll explain why I ask if you can.