What will happen to the card when it is exposed to a powerful magnetic field, for example, in an MRI machine? What is the probability that the wallet will demagnetize and stop working?

The chip doesn't contain any magnetic elements that could demagnetize. Moreover, the Tangem card chip is protected against EMPs (electromagnetic pulses), ESD (electrostatic discharge) and X-rays in compliance with the ISO 7816-1 standard.