AirPort Express on a new ipad

Yes - but due to a known issue with the Airport Express, you may not be able to use the most recent version of the AirPort Express firmware (7.8.1).

Assuming that you are currently able to use AirPlay to stream audio to the Express, don't update the Router firmware to a more recent version. While old and no longer supported by Apple, these versatile little Routers support capabilities not found on more recent Apple Routers, such as the later AirPort Extreme.

You'll also be pleased to learn that the AirPort Utility App, used to manage the Router settings from iPad and iPhone, remains available for download from the Apple App Store - and is fully useable under iPadOS 18.x.

https://apps.apple.com/app/airport-utility/id427276530

You mean one of these?

AirPort Express 802.11n (2nd Generation) - Technical Specifications - Apple Support

If so, it's pretty old and long in the tooth, but i see no reason why a new iPad shouldn't work with it just as an older iPad did.

Regards.