You can still browse the internet. Safari still works. I have ancient 1st gen iPad Air and I use it for that; you can still watch YouTube (from the web), it still works fine. Anything that has a web app mostly works.

If you manage to install decent apps in time, you can use these as e-readers or video players. But batteries will eventually fail and all what you'll have will be a fancy fragile chopping board.

I was gifted with iPad 1, Air 1 - first won't charge for 6 years now and data I didn't synchronize are gone, second one needs a serious "warm-up" before charging and while Apple released 12.5.8 in the end of January, it won't get any new apps.

I have a 3rd generation iPad from 2012 [1]. The battery is still very decent after 14 years. It has a retina display and a remarkably good speaker, so I use it for e-books / audiobooks, podcasts, music (on device) and sometimes playing around with synth apps (nano studio).

The bad stuff:

- iOS update with the parallax effect (iOS 7, I think) came soon after this iPad was released and made the device feel extremely sluggish (even with effects disabled). I was very pissed (downgrade not possible). It's on iOS 9 now, still as slow. The apps I still use work ok, but switching between them is a terrible experience.

- Can't update iOS any further. Can't install any new apps. Certificates expired, so can't use any webbrowser anymore (no https) and a few months ago even podcasts stopped downloading (books and music I upload via cable).

Notice how the good stuff is all hardware, while the bad stuff is all software.

[1] https://support.apple.com/en-us/111992

You can jailbreak it and attempt to bypass app restrictions (e.g. with 3dappversionspoofer). Ymmv. https://ios.cfw.guide describes how to jailbreak.

Why can’t you still use it?

You just won’t be able to download new apps as they bump their minimum.

Wait for a trade in special and take advantage of it. Or use it for safari only.

Use it as a control center for your home automation.

maybe use as a e-reader or watch ripped media on it? if it's jailbreakable i am sure there's a lot of stuff to do too

I don't think there is? I'm holding onto them in the hope that there's a good solution in the future.