Hello Everyone,
The Utility Network User Type extension is included in your Portal license you generate from My Esri (this will include this as well as your creators/viewers/app bundles/etc).
If you do not see the Add-on user type extensions section when creating the Portal license (same step as where you select how many creators/viewers/etc) then I would recommend reaching out to your Customer Service Representative to see if you are entitled to this license via your license agreement with Esri.
There is no extra steps or unique workflow for Utility Network licensing 10.8+beyond. Either you have the option to include it in your Portal license or you do not (same as with insights licenses, app bundles, etc). If you do not see this option, then I recommend reaching out to your customer service contact to see what you are entitled to.
Afterwards, import your Portal license into your Portal following the standard workflow. then you will see the option to assign this user type extension within your Portal.
Thanks!
Travis