This is a general scenario I came across specifically in terms of migrating a flow from Dev to UAT or PROD environment.
When ever we try to export and import flow from one environment to another, it always need to update site url in all the actions wherever used.
It will be wonderful to have a predefined action which will work list a assigning a site URL to a variable. which will be validated else rejected, and of-course then used in all the SharePoint related actions wherever necessary.
This will avoid update in each action post flow import into a new environment.