I've heard about https://btcpayserver.org/
Discussion
BTCPay Server is NOT a point of sale system.
Oh, POS is that things that report what your'e selling to govt. isn't it?
Its not a system that integrates for things like inventory, reporting, employee auth for access, backend.
Clover added support for BTC years ago for mainchain but not enabled in most places. Last I heard they were working with Strike on the Lightning side.
Same with Blackhawk and NCR.