Well you’d need to know the total amount of data to load and then incrementally keep track of how much of it has been loaded. It’s probably waaaaaay more work than it’s worth. I’d imagine that it would have be be some extremely low level coding to keep track of it all.
If you’re streaming levels, do them in chunks by sub leveling the map. Have a sub level for primary static meshes, one for secondary SMs, tertiary SMs, lights, particles, sounds, etc etc. Stream them in one at a time and you’d be able to make more of a progress bar for them. It would be up to you to set how much % worth each sub level is though.