As in they no longer offer updates, support or repairs for it - it still works, but you're on your own.
Right. I have one that I use with my M1 MacBook Air in clamshell mode, and it's pretty nice, but I do need to replace the built-in Thunderbolt cable, since it's not that reliable anymore. For now I am getting by using the Thunderbolt port on the back, hooked up to a Thunderbolt 2-to-3 adapter connected to my CalDigit TS3-Plus dock. Shouldn't be too hard a replacement job for me, given I do this kind of work a lot at my job. Then once I get an M2 Pro-equipped Mac Mini, I can use the Thunderbolt display with it, but I won't need the dock, as I can just hook it up to one of the four built-in Thunderbolt 4 ports using my 2-to-3 adapter. (I'll most likely still have the dock hooked up to another one of the TB4 ports, for when I need to import from SD cards or analog line-in audio and whatnot.) Even the Display's built-in FireWire 800 port I find useful for when I am archiving/importing MiniDV or Digital8 tapes...
...such as this YouTube fursuit vlog I did demonstrating the older camcorders'
tacky built-in effects. That way I don't have to always daisy-chain my TB 2-to-3 adapter to my FireWire-to-Thunderbolt adapter (and that method DOES work, by the way).
As for the first-generation iPad Air, I'm kind of not surprised. We're getting a LOT of them from school districts retiring them in favor of newer iPads and/or Chromebooks (just like a couple years ago when Apple announced the iPad 2 as being obsolete and we began getting hundreds of them from schools) and after a while we got so many that now I have to log any with noticeably physical damage (cracked front panels, heavy scratches, engraving on the back) as not worth re-selling online; once these damaged models are wiped and reset, I prepare them to be recycled. But still, it's amazing how the iPad Air replaced the "regular" iPad in 2013 and eventually influenced the "regular" iPad once that was revived, to the point where the current iPad Air is basically a "lite" version of the iPad Pro, and the "regular" iPad is like the original Air.