I have used Armory wallet in the past and some value is stored in a (Ubuntu) machine which is currently unused. I would be most grateful for comments on how to proceed,
Install the latest version of Armory 0.95.1 and the latest version of Bitcoin Core. It should work and you will be able to access your bitcoin. If armory was previously installed, You will need to delete the folder named databases in the armory data directory as the database format has changed.
because I see that this wallet is not currently under development (?).
Armory is still being developed. It is under the development of a new maintainer. The development progress has slowed significantly because the company previously behind armory stopped working on it.
You might be able to move the file to a windows machine running armory
I do not recommend that you use Windows. Armory works better in a Linux environment like Ubuntu.
Note that a watch-only copy of a wallet uses the same private key as the original wallet it was created from.
Watch only wallets do not have private keys. They only contain addresses and public keys.