I think you can pick these three sites [1] [2] [3], I read they're accepting many crypto including USDT. But I'm not sure if they accepting various chains, at least they accept USDT ERC-20, only few sites are accept TRC-20 or BSC network.
I wouldn't recommend shoppy.gg
He didn't ask a review about shoppy.gg, he ask about the alternative.
I recommend checking out Shopify. They have a wide range of options for accepting different payment methods, including USDT.
But the site need a third party help e.g. exchange in order to accept crypto.
[1]
https://en.cryptoprocessing.com/[2]
https://triple-a.io/[3]
https://gocrypto.com/
