iPad

iPad 7th/ 8th gen has a nearly 10-1/4 inch diagonal screen ( 10.2 inch diagonal screen ).

iPad Air 4 has a nearly 11 inch screen ( 10.9 inch diagonal screen that is nearly 3/4 inch bigger on the diagonal than the iPad 7th/8th gen).

iPad 7th/8th gen uses the old iPad design with much wider outer black bezels.

iPad Air 4 has much narrower bezels similar to the newer 2018/2020 iPad Pro design look.

iPad Air 4 has a much more powerful, sophisticated and much faster internal CPU ( Central Processsing Unit ) than the 7th/8th gen iPad.

iPad Air 4 uses the NEW A14 CPU. The iPad 7th gen uses a much older Apple A10 CPU ( found in the 3-year old iPhone 7th gen ).

iPad 7th/8th gen has internal 3 GBs of internal processing RAM ( Random Access Memory ).

The iPad Air 4 has 4GBs of this internal processing RAM.

iPad 7th/8th gen comes in 32 or 128 GBs ( Gigabytes ) of internal data storage models.

Actual, usable, practical data storage space of these storage models is approx. 22 GBs and 111GBs, respectively.

iPad Air 4 comes with 64 or 256 GBs of internal data storage space which doubles the available data space of the iPad 8th gen.

Actual, usable, practical data storage space of these storage models is approx. 56 GBs and 234 GBs, respectively.

When purchasing any Apple iOS device, purchase the largest internal data storage space model you can afford as internal storage of Apple mobile devices IS NOT EXPANDABLE!

iPad 7th/8th uses Apple's old a proprietary and slower Lightning port/connector and Lightning cables for charging and for external accessory connection and data transfer.

The 2020 iPad Air 4 uses the industry-wide data transfer USB-C protocol which is much faster as has much easier to connect and use external accessories and easier and faster data transfers via external USB-C drives.

The iPad 7th/8th gen has a two speaker ( non-stereo ) speakers on one side of the iPad and a mini jack headphone input to plug in wired headphones.

The 2020 iPad Air 4th gen has true stero speakers on either side of the iPad the use two additional resonance chambers.

For audio, the 2020 iPad Air 4 needs special, optional USB-C to Lightning or USB-C to 3.5mm headphone jack for wired earbuds/heqdphones OR Bluetooth audio earbuds or headphone ( with bulit-in microphone ) for listening to music/audio or for using the iPad for isolated FaceTime calls or audio calls from an iPhone.

IPad 7th/8th gen uses the 1st gen Apple Pencil.

iPad Air 4 uses the newer 2nd gen Apple Pencil which is more expensive.

iPad 7th/8th gen has a non-laminated screen where glass and touch display screen underneath ARE NOT glued/bonded together resulting in a tiny air gap between glass and the touch screen.

iPad Air 4 HAS a bonded/laminated glass and touch screen with extra screen options, such as better color saturation and the ability to auto control the screen's white color balance based on external environment lighting conditions.

Hope this helps in your iPad decision making process.

Best of Luck to You!