Here are the guides that helped

https://www.expressvpn.com/support/vpn-setup/share-vpn-connection-mac/

https://support.purevpn.com/internet-connection-sharingics-on-mac

https://wiki.it.ufl.edu/index.php?title=L2TP_VPN_for_Windows_10

TLDR:

On a Mac: 

- System Preferences

- Networks

- +

- Interface: VPN

- Service Name: MY_CUSTOM_VPN

- Service Address: l2tp.vpn.ufl.edu

- account name: 

- Authentication settings:

- Password:

- Shared Secret: 

 - Advanced -> Send all traffic over VPN connection

==========

Click connnect

==========

- System Preferences

- Sharing

- Internet sharing

Share your connection from: MY_CUSTOM_VPN

To computers using: Wifi