Static magnet fields won’t do any harm to RFID and NFC implants.
Only high frequency magnetic fields with a frequency around the one of the implant could damage it.
Induction cooking fields or wireless mobile chargers have been reported to be problematic in some cases for RFID chips as they operate round the same frequency.
For NFC i don’t think you would encounter such issues as the frequency is much higher and high power magnetic fields are rare there.
However, if you encounter strong magnets a lot, take care to not magnetize the core of the implant as that will decrease the reading range by a lot. (You should be able to demagnetize it)