You can use BTCPay integrated with Payjoin [1] to make your transaction will not linked with each other, but you need to host yourself to run BTCPay with some requirement 4GB RAM and 500GB hard drive [2]

But the problem of BTCPay with Payjoin transaction is most of wallet still doesn't support Payjoin, because your customer should use a wallet that support Payjoin or the transaction will be linked.

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[1] https://docs.btcpayserver.org/Payjoin/
[2] https://bitcointalk.org/index.php?topic=5259548.0