Would like iPad Air adapter to use iPhone 7+ earplugs

How would a 3.5mm adaptor work with lightning headphones?

The OP said iPhone 7+, so presume that means iPhone 7 plus

https://support.apple.com/kb/SP744?locale=en_GB

Box contents of iPhone 7 Plus -

In the Box

• iPhone with iOS 12
• EarPods with Lightning Connector
• Lightning to USB Cable
• USB Power Adapter
• Documentation

So the supplied apple headphones would have lightning connector.

So would need a USBC to lightning adaptor not a USBC to 3.5mm adaptor

Wouldn't work as the iPhone 7+ uses a lightning cable, no headphone jack

I couldn't remember when Apple stopped shipping the old wired earpods in iPhones and discontinued the 3.5mm headphone jack.

My wife's old version iPhone SE came with a pair of Apple wired earpods and that SE version was introduced in early 2016.

The iPhone SE was probably the last iPhone model to still have the headphone jack.

My bad.

I have not seen a USBC to lightning adaptor

It sounds as if the Poster wants to use the once supplied Apple wired earpods with their new iPad Air 4.

That adapter will work with the wired Apple earpods.

Never mind.

Not sure what cable or adapter the Poster needs.

Found one on Amazon.

Anker USB-C to Lightning Audio Adapter

https://www.amazon.com/Anker-USB-C-Lightning-Audio-Adapter/dp/B07R6MKJZH/ref=sr_1_3?crid=1W9M2S8US969L&dchild=1&keywords=usb-c+to+female+lightning+cable+adapter&qid=1608496272&sprefix=USB-C+to+female+Lightning+%2Caps%2C179&sr=8-3

Apple USB-C to 3.5 mm plug here.

USB-C to 3.5 mm Headphone Jack Adapter

https://store.apple.com/xc/product/MU7E2AM/A