macOS Sequoia 15.3.1 Share VPN to Windows Laptop

TL;DR

L2TP is a must. WireGuard and IKEv2 are not supported.

Background

I have a personal MacBook running macOS Sequoia 15.3.1, and a Windows 11 laptop managed by my school. While using a public Wi-Fi, I want my MacBook to share the VPN to the Windows laptop.

When MacBook is connected to Wi-Fi, it can only share Internet with Ethernet

Physical Set-up

A USB-C hub adapter needs to be connected to macbook to provide an ethernet port. My Windows laptop doesn't have an ethernet port,so we need the second USB hub adapter.

macOS Set-up

Settings -> VPN -> Add VPN Configuration -> L2TP over IPSec

L2TP -> Options -> Send all traffic over VPN connection

When the L2TP VPN is added and enabled, we can share the Internet now.

Settings -> General -> Internet Sharing -> More

In the config dialog, set Share your connection from to Wi-FI, and enable AX88179A.

Enjoy!

Epilogue

When MacBook is connected to Wi-Fi, it can also share Internet with Thunderbolt. Sadly, my Windows laptop doesn't have one.

iPhone's USB tethering is limited. Only the cellular connection can be shared. link

Vanilla Android doesn't route VPN traffic when tethering link. Modified Android like AOSP may have an option Allow clients to use VPNs link1 link2. After rooting, there are several apps doing so, including VPNHotspot. Sadly (again), my Samsung Tablet at hand can't unlock bootloader.