How did you deploy to the web app? And is it currently in a healthy state? Windows or Linux? .NET? If you go to the overview page > diagnose and solve problems and check these areas for obvious errors on the functionality of the web app:
Alternatively, it may be that you're just trying to upload a .htm file into wwwroot manually? and not using a framework like .NET. If so, I am not sure if that would work. You can look into Azure Static Web Apps (different product to Azure Web App) or Azure Storage for static content if that is your goal specifically without a framework, see more:
- https://learn.microsoft.com/en-us/azure/static-web-apps/overview
- https://learn.microsoft.com/en-us/azure/storage/blobs/storage-blob-static-website
Otherwise if you are looking to go ahead with Azure Web Apps, then take a look at this, and maybe it will nudge you in the right direction:
Let me know what you find, and we can try and work it out together :)