We mostly BTCPay for these requirements, self hosted and removes any intermediaries which is what crypto was designed for, it's also used by some of the largest sites on the web so well tested.
We are looking for select stores to participate in testing a crypto gift card checkout module/system. This is invitation only. DM me should you have interest.IMO, BTC and ETH are difficult mediums to use for payments, because of the fluctuations. Stable-Coins are more ideal for merchants.