The “old” Numbers/Pages/Keynote apps won’t get any further updates, but my iPad is so old that it’s stuck on iPadOS 17, which is lower than the minimum requirement of the new versions (18 or higher).
So far I did not feel tempted to upgrade my iPad, but if this means I can no longer share documents between my iPad (old apps) and iPhone/Mac (new apps) I might have to…
Did Apple say anything about the data format compatibility of old/new Numbers/Pages/Keynote apps?
(It looks like I won’t be getting 1Password updates either on that iPad; this might trigger me to buy a new iPad after all these years)
Apple doesn’t tend to talk about cross version compatibility. The impression I always get is that they expect everyone to upgrade to the latest and greatest.
As far as I can tell, the format has been consistent (in the forward direction) for at least the past 10 years. At one time Pages couldn’t import from the format two versions before, but that’s all fixed now.
Note that you should never expect documents created/edited with newer versions to be usable with older versions. That tends be true no matter what the program, not just Pages/Numbers/Keynote. So you can still create on your old iPad and edit on your Mac, but you can’t take the document back and edit on the old iPad.