iPad Air 4th Generation SIM Card Slot not working

For models that support eSIM, this is certainly an option.

Note, however, that iPad's originally sourced from a Cellular Provider (such as AT&T in the US) may have had their eSIM permanently disabled. If the iPad was purchased directly from Apple, without being initially tied to a Cellular plan, should not have this potential limitation.

As described, your iPad has likely developed a hardware fault.

You would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad. If a fault is confirmed, you'll be in the best possible place to explore your available options.

Genius Bar Reservation and Apple Support Options - Apple