Could you please give more details about your issue? If the Excel could not loading, it may cause by the network or the connection of Excel connector, you can check the network and try it later or recreate a new connection of Excel connector.
If possible, please upload the screenshot about your Flow configuration, it will help us better to assist you.
Community Support Team _ Lin Tu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.
Not sure where my original post went, but here's a quick recap of what I originally wrote:
When loading the Flow for Excel Online add-in, the panel which usually shows the flows to run is blank.
We tried multiple browsers, computers, and even another doc that has the flow add-in connected to it as well. All of them are showing a blank panel. This is happening to multiple flows, not just one so I'm not sure it's tied to the configuration unless it's an issue with all Excel Online connectors.
We did find out clearing our browser data brought it back temporarily. However, it went away again about an hour later.
We also found out that loading the sheet in an incognito tab allows it to load.
This seems to be the workaround for now, but it's definitely not a long-term solution.