When Design Review is not installed, (at least in Vault 2022 and 2024), there is an error saying Design Review is not installed, and files cannot be viewed unless the user knows to go change the viewer option.
Automatically toggling the viewer option to use Autodesk Viewer when ADR is not installed would help with user experience - the files could still be viewed.
That toggle in Options could also prevent/disable choosing ADR until installed.