Web app large uploads and downloads

Folks (anyone working?) I've been asked to add a feature to a Blazor Webassembly app to allow uploads and downloads of possibly large numbers of files between the local file system and Blob storage. I'm not sure how to implement this feature in a browser hosted app. I wrote a WPF tool for "managers" which does high-performance bulk uploads and downloads with nice progress (the code is trivial on the desktop), but now they want the same feature for "normal" users in the Blazor app. Given how dumb and restricted browser hosted apps are, I don't know how to code this, or if it's even feasible. Are there some tools, techniques or tricks I can apply? Any ideas or suggestions anyone? Thanks, *Greg Keogh*