You have a custom SharePoint Site Design, which executes (through MS Flow or Azure Logic App) PnP Provisioning process. You want to notify users that the site is not fully ready yet and it's still being updated (by background provisioning, which might take a long time). One option is to use two-way interactive communication between the SharePoint web site and the job using SignalR. That's something we're going to explore in this post in great detail.
Check out below short video, which demonstrates the resulting UX we're building in this post:
The video was cut because the actual process takes 7-9 minutes on my tenant.
Read further below to find out how to setup everything from scratch.
All sources, as well as brief configuration steps, are available at the GitHub repository. More...