This is not so much a Cubase problem but a Kontakt/Native Instruments problem. Native Instruments are pushing hard their native access update thing. They want people updating all the time. This is a problem though. If you’re working on a single or album with a tight deadline or for an important client, it’s unlikely you’ll want to update your version of Kontakt. But if your colaborating with someone at the same time who is using a newer version of Kontakt, you’re forced to update. Otherwise when you open that session back in your studio, you will see the message you mention when opening the session stating that your version of Kontakt is too old. So then you update and then if you collab with someone else with a older version of Kontakt, now they are forced to update. It like an update virus lol.
You will also see the message you mention when you load a Kontakt instrument that has been created by someone who is using a newer version of Kontakt to you.
All versions of Kontakt ‘should’ be backwards compatible but almost none of them are forwards compatible. I don’t see why they can’t do this since these are usually just tiny .1 version updates that seem to break forwards compatibility but sometimes the updates are nothing but minor bug fixes.
You can try copying the old Kontakt VST in the your VST folder to somewhere else, renaming it and putting it back in after the update and they might both work side by side but I haven’t tried it. I think in the past though I had Kontakt 4 and Kontakt 5 running side by side. If you’re worried about Kontakt and things going wrong you can do what I do which is clone your entire OS via Acronis. Should anything happen, you can re-install. It’s best to have your OS on a separate partition or drive to you session files and data for this reason as it’s easy to clone and wipe if needed in an emergency or tight deadline.
Anyway, if you’re getting that error for a particular project or instrument, the only fix is to update your version of Kontakt.