I’ve installed the new DT to Go, and find the old one is still out there. Can I safely delete it from my iPad and iPhone?
Yes, if you’ve opened DTTG3 and data has automatically migrated. (PS if you haven’t already, you should update to 3.0.3)
As assumed. Also assumed–that the app updates itself; but how can I actually find the version number of the app?
Tap on ‘?’ on the bottom toolbar while looking at the ‘root’ menu (the list of your databases) for the version number and the release notes.
Excellent. In fact I am at v3.0.1 on the iPhone and v3.0.2 on the iPad. Curiously, the Apple Store provides no more current version.
In response, I’ve rebooted both iPad and iPhone and neither changed. Additionally I do not find the same display as you provided within the Apple Store for either mobile device.
No matter, I’m confident it will all sort itself out over the next few days. I’m good with that.
Okay. Let us know if this persists.
FYI, I have at times had to refresh the list of installed apps with updates by pulling down on the screen showing available updates (App Store > Account).
On my iPhone I see no way to access app store > account within the updates screen or anywhere else (IOS v14.4).
Tap whatever icon is to the right of Search in the upper right corner of your screen.
On the search screen the upper right-hand icon is my own user-image. Had no idea this was here. Thatnks to both of you!
App Store seems to have become quite flaky about showing updates lately. I think they eventually happen, but quite often I know there is an update which is not showing.
What always works in these cases is use Search to find the app. Then click on it to show the full detail for the app. In this window the usual “Get” turns to “Update”.
It should be enough to tap on the image in the upper right of the app-store screen (ie your user image) and then drag down on the window which opens up. That refreshes the update list.
It should be …
I know…emphasis on “should be” . It is sometimes. 
Actually I have the opposite question: is still possible to download on an old machine a DTTG version 2?
TIA
No, DEVONthink To Go 2.x is not available to the public.
actually I bought it…
It’s inadvisable to run the 2.x release as it is long out of development and support.