As KARFA and vintagepilot say, AMEX 2-4-1 vouchers have had various extensions, but these have been in the form of having 6 months added at a time, or at the time of issue. They have not been universally extended to Sep '23

You may have some 2-4-1s which, even after extensions, are due to expire in the coming months.

If you wish to save them, you can book the cheapest 1 way flight you can find, e.g. an economy domestic and then immediately cancel the booking to convert it to a future travel voucher, which effectively keeps your 2-4-1 alive past its expiry date until the validity of the FTV, i.e. Sep 23.

A coupe of caveats - choose a flight before the end of Aug this year so Book With Confidence applies and you can convert the booking to the FTV. Also, you will lose flexibility on passengers, only go down this route if you know which 2 passengers you want to use the voucher on. As Globaliser has noted, this then makes the validity of the 2-4-1 effectively that of the FTV.