Someone named Victor Weiss built a Point of Sale overlay for BTCPay Server.

Looks like they made it pretty slick. Restaurant owner needs AQUA Wallet (so you are using Liquid), but you can accept lightning payments for your menu items.

They don't say it on their website, but I'm guessing the way it works is that BitBite is hosting an instance of BTCPay Server and the merchant is just connecting their wallet to it. But as far as a realistic way for a food truck or small restaurant to start accepting bitcoin payments, this could work.