iPad OTA pushed update
Not an expert on how iOS/iPadOS OTA works, but my understanding is that it depends on whether or not the update has been locally downloaded yet.
If you check Settings &gt; General &gt; Storage and see the iPadOS 14.3 update somewhere in that list (where in the list it is depends on how large it is relative to other files/apps on your iPad), it's been downloaded locally. You should be able to update to it, as the locally downloaded copy should be signed.
If you don't see the update file listed, it's likely a cache issue and pressing the button will likely cause it to refresh and download iPadOS 14.4. Some older updates (back when OTA was newer) acted as bridge updates to newer versions, but that's not been the case since well before iPadOS was forked from iOS.
Again, I can't say with any sincerity that this is all true and correct. What I can say with sincerity is that you shouldn't update at all if you're not 100% certain that you have saved blobs and are willing to potentially lose your jailbreak.