It sounds like you replaced the wifi flex and not the NFC flex. Check for corrosion or damaged flex cables around the Wireless NFC Charging Flex and connector on the motherboard sometimes the foam around the connector gets in the way of the pins. It's an inexpensive part so I would just replace it. If that doesn't fix it then your NFC IC chip on the motherboard is probably fried. It's very common for the NFC charging flex to get damaged during back glass repairs so I would bet on that being the issue.
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