I made this suggestion in Parcel Fabric recently and it was elevated to Under Consideration:
Allow the selection of earlier version of Parcel F... - Esri Community
I would also like to make the same suggestion here for Utility Network, as it too is directly tied to a version of ArcGIS Enterprise, which makes managing it incredibly difficult, especially if you upgrade your ArcGIS Pro regularly to take advantage of new/updated features. Because you are forced to use earlier versions of Pro because you haven't upgraded your Enterprise yet, tying a UN to a specific version of Enterprise also forces you to use earlier or outdated versions of toolsets like Utility Network Package Tools and Data Loading Tools, which restricts your ability to use updated versions of those toolsets.
As I indicated in my idea in Parcel Fabric, organizations do not upgrade Enterprise software like ArcGIS Enterprise every release because it is not just as simple as upgrading a desktop application like ArcGIS Pro. You have to plan out in advanced, weeks or even months, because the upgrade will affect every user in the organization globally and you have to prepare your users and your network appropriately.
Presently, I have to have a single computer host a downgraded version of Pro just so I can manage our UN. This is not an effective or efficient use of our resources and is a hidden cost for most agencies. Please consider either not tying the UN version to Enterprise, or at the very least, provide the option to choose your version of UN from whatever version of Pro you are using so that GIS systems managers like myself do not have to allocate additional resources just to manage them.