I know there was some project about this but haven’t heard of anything for a while. Ewaste is such a crime; all of my devices are used or older purchases that are past their “cool by” date. I have an iPad 2 and iPad mini that function perfectly but aren’t supported by apple anymore. Would love to get a second life for them instead of having to get rid of them for no good reason.
Getting a Linux mobile OS on it would probably have a lot of issues, Ubuntu touch for example just supports the most popular phones as of now.
However it would work in theory you’d have to do some really weird low level gymnastics and one shot the execution to run Linux natively.
Alternatively you could use a VM to run Linux and try to work around that.
https://ipadlinux.org/
Disregard that, I see that the iPad 2 and iPad mini are not eligible since the min iOS version is 11. All devices since 2012 work though, hope that helps someone else. Sorry.
See here for a table https://iosref.com/ios