Catalina 10.15.5 Slow File Dialog Since the 10.15.5 Catalina update, file dialogs in my system are extremely slow. It can easily take a couple of minutes to be able to save something to the disk. Never had a similar problem before. 

Ran a disk check, made sure that I have free disk space (more than 400GB).

Otherwise, the machine is running smoothly, without any other issues.  

Tried googling around and found out that there was a similar issue back with Sierra. Tried to apply the proposed fixes, but to no avail. 

In Safe Mode the problem doesn't appear to persist.

Any suggestions would be greatly appreciated! 

Machine specs: Mac (Retina 4K, 21.5-inch, 2017), 3,4 GHz Quad-Core Intel Core i5, 8 GB 2400 MHz DDR4, 1TB Fusion Drive.

Update:
No finder extensions installed. No OneDrive/Dropbox/anything like that.

    kextstat | grep -v com.apple
    Index Refs Address            Size       Wired      Name (Version) UUID &lt;Linked Against&gt;
  102    0 0xffffff7f80f2d000 0x6c4000   0x6c4000   com.realtek.driver.RtWlanU (1830.32.b13) E254FC27-6491-3BC2-BBE8-1B529EA778CD &lt;57 18 6 5 3 1&gt;


Update 2: 
It takes roughly 90 - 120 seconds to a Save or Open dialog to become active. While it's stuck, the CPU usage by the process gets close to 100%. Doesn't matter the application I'm using - QuickTime, Pages, Microsoft Word, Photoshop or Safari




Update 3:
Booted up in the recovery mode and reinstalled Catalina keeping all the computer data. The problem persists

Update 4:
Installed BitDefender Trial version in order to make sure there is no malware/virus/whatever on my machine. 90 minutes later - nothing found, but the problem persists.

Update 5:
Configured a new administrator account on the Mac. While configuring it, unchecked all iCloud features - the problem doesn't reproduce using that account. 
Updated the new account with iCloud settings (photos sync, documents sync), the problem doesn't appear.
I spent about a year working with Apple technical support on something that sounds just the same. The good news is that, assuming your problem is the same as mine, there is an easy fix.  The challenge in diagnosis is that some interaction between iCloud and the Finder appears to be involved. iCloud's involvement is why problem persists across reinstalling the system, etc.

They fix was to delete either the dyld shared cache or the XPC cache. Unfortunately, I can't remember which it was and can't find my notes from then. But, since they are both just caches, there is no harm in deleting either or both.

The best way I found to do it is to download the Onyx app (free from https://www.titanium-software.fr/en/index.html). Under the "Maintenance" tab withing Onyx, you'll see the option to delete either or both of those caches. Do so, reboot and see if your problem is fixed. Once I did this, it fixed the problem entirely and it hasn't reappeared in over 2 years. There is probably a way to do this from the Terminal (indeed, Onyx is mostly just a wrapper over command line functionality), but Onyx worked great for me.  I hope this helps you.