GL-SF1200: How to setup VPN to allow my friend access to my internet?

You can definitely run a VPN server on your router using the free GL.iNet DDNS service, which is used by other people on this forum.

I am not a legal expert, so I searched out some information.

https://nordvpn.com/blog/united-arab-emirates-vpn-guide-2022/#:~:text=your%20usual%20websites.-,Is%20a%20VPN%20illegal%20in%20the%20UAE%3F,censored%20by%20the%20UAE%20government.

3 Best VPNs for Etisalat & UAE That Still Work in 2022.

If my non-expert understanding of these posts is correct, then VPN is not illegal in the UAE, but accessing banned websites, services, etc. is illegal and connecting to your router VPN to use VoIP would be illegal, at your friend’s own risk.