How to view download progress while Finder downloads new iOS version?

In macOS Catalina, the iOS devices are synced and updated using the Finder instead of iTunes.

Is there a way to see the progress of the iOS-download in Finder?

Unfortunately there's no immediate way.

But see this article: https://discussions.apple.com/thread/250790312

While there is no progress bar available, one potential way to estimate the progress is through Terminal, with the following command:

ls -lhrt ~/Library/iTunes/iPhone\ Software\ Updates

It will show the size of the current (.ipsw.download) and all previous (.ipsw) update files, which can be used to estimate progress. For example, for a 2.9G update file (can be estimated using previous update files), if we see that the current update file size is 2.3G, then the progress would be approximately 2.3G / 2.9G = 79%. By running the above command periodically, we can somewhat know how long it may still take (or at least the downloading is still in progress and not stopped because of network or other issue).

In addition to Joe Farina's answer, you can also get a rough idea of how quickly things are progressing from Activity Monitor's Network tab.

Look for AMPDecivesAgent, which should show you how much that process has downloaded. This is probably ** (but not guaranteed) how much of the latest update you're downloading has downloaded.

If you're not downloading lots of other things, you can also see the speed of your download at the bottom of the activity monitor (in blue in the image below).

** Note that this is actually the total downloaded by that process, so if you're downloading multiple updates or have recently downloaded an update, that will be included in this number.