Finder and Open&Save Dialogs Hanging/Freezing after Catalina Update

Try one of the standard fixes: boot into Safe Mode (How to use safe mode on your Mac - Apple Support) by booting with the Shift key held down and check there to see if the problem persists.  Reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Download and run Etrecheck. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Add Text button to include the report in your reply. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

IMPORTANT:

Before running Etrecheck assign Full Disk Access to Etrecheck in the Etrecheck's Privacy preference pane so that it can get additional information from the Console and log files for the report:

Also click and read the About info to further permit full disk access.

Then we can examine the report and see if we can determine what might be causing the problem.

You've installed what most of the experienced contributors to these forum consider akin to malware: CleanMyMac. There is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus or security apps on your Mac.  This user tip describes what you need to know and do to protect your Mac: Effective defenses against malware and other threats - Apple Community   

Uninstall CMM according to the developer's instructions. Then you can check to see if you've removed all of the supporting files by downloading and running Find Any File to search for any files with the application's name  and the developer's name in the file name.  For CleanMyMac you'd do the following searches: 

1 - Name contains cleanmymac

2 - Name contains macpaw

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

You should limit the number of apps in the System/Users & Groups/Login Items preference pane to only those that you must have at login. The others can be launched when needed and closed when done.

The crash section of the report shows a fair number of apps crashing multiple times. This may be due to CleanMyMac so run for a while after it's been removed and then rerun Etrecheck to see if those apps are still crashing or not. If they are make sure they are up to date and compatible with Catalina.

I found this discussion when I searched for 'generateImageWithRequest' which I found in a spin report for Finder.

We have similar spin reports - lots of time spent trying to get images. In my case, I was trying to view the /Applications folder of a networked machine. After the spinning subsided, I tried visiting a directory with plain-ol folders, and it loaded quickly.

So, my theory is that we're waiting for Finder to pull images from the remote system. /Applications is probably the worst-case scenario as I'm guessing Finder doesn't have icons stored for these .app file types. It must be pulling them from the Application metadata for each and every app!

You will also see this if you are browsing a folder with images / video as Finder will try to pull thumbnails. However, I do notice some media files displaying something briefly and then overlaying the thumbnail - could it be an asynchronous fetch? It should be...

Hmm, Finder has been spinning like crazy and I have gotten a few good samples... All of them point to getting file attributes (name, image, etc.).

Time to file a bug report... Also, a different problem but related, if you view a remote directory containing images, photoanalysisd fires up and starts doing its thing (looking for faces, etc...) chewing up a lot of CPU. Hmm.. if only I knew some folks over there ;)