This is a great blog from Hackaday that shows how old iPads that are no longer usable can have their screens used as standalone monitors. Since Apple are openly criticised for their throw away culture it’s a reasonable way of keeping these old units out of landfill, and saving you some money as well. I love the example of using an old screen as an additional screen for an iMac.
Turning surplus LCD panels into stand-alone monitors with the help of a driver board is an established hack, and a search of eBay or AliExpress will …
Old iPad To New Screen
Foxes Den 
I tried to use an old iPad as a digital photo frame but it was a bit flakey
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I use one in our garden pub as a darts score board. Better than anything on offer doing the same job 👍
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