verify fusion drive

Your Mac is a mess.

Notes:

• Failing Hard Drive. Backup all data ASAP!
• Follow the EtreCheck prompts to remove orphan files.
• Delete CleanMyMac. [Instructions]
• Delete Intego. [Instructions]
• Delete Bitdefender. [Instructions]
• Try not to use Paragon software.
• Delete Viscosity.
• Delete Seagate software, unless it is really needed for some reason.
• Delete all other VPNs.

But, here's your BIGGEST issue:

Performance:

System Load: 2.29 (1 min ago) 1.91 (5 min ago) 1.84 (15 min ago)

Nominal I/O speed: 2.20 MB/s

File system: 3279.29 seconds (timed out)

Write speed: 26 MB/s

Read speed: 54 MB/s

Your Fusion Drive is failing. You essentially have two options from here:

1. Go to the Apple Store and get the Fusion Drive repaired. Start the repair request here: Get Support.
2. Use an external SSD and run macOS from that. If you're interested in this, please read: How to Setup and Use an External SSD as y… - Apple Community.

-Jack

Your screenshot suggest to me that the new file system structure was properly resotired.

Were the drive "split," that is, it lost the software connection between its SSD component and its mechanical drive component, it would not identify as "Fusion" in Disk Utility, so I thing that is not the problem. These two article discuss 1) the new file system structure, and 2) how to identify and fix a split Fusion drive.

About the read-only system volume in macOS Catalina - Apple Support

How to fix a split Fusion Drive - Apple Support

Given that fact, and the limitations of helping in a venue where we can neither see nor touch your computer, the best way we can look for so other issue causing the intermittent slowdowns is for you to post a snapshot of your system configuration. Fortunately there is a safe, secure way to do that. 

We can quickly and within the limitations of these forums help you determine what issues are at play if you use EtreCheck Pro, available here:

https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues, and RAM usage. Etrecheck is the development of a long-serving and trusted contributor here expressly for displaying information in these forums to help us help you. It will not reveal any personal or secure information.

Run it, select “Report" from the left-hand pane (scroll down to the bottom of that pane to find):

When its report displays, click the "Share Report" icon from EtreCheck’s toolbar and then "Copy report” from the resulting dropdown.

⚠️ Please DO NOT highlight the text in the report before using Etrecheck’s “Copy report” command—that will garble the formatting and make the report slower and harder to evaluate.

NOTE: Changes in late 2018 to the forum software require you use the “Additional Text" icon (see example below) to embed the report into a post:

Paste the report into the resulting “Additional Text” window:

No wonder you're having so much performance issues. You've installed a bunch of junk ware. First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is desshoigned solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Also, unless you're using a true VPN tunnel, such as between you and your employer's or bank's servers, they are useless from a privacy standpoint: Public VPN's are anything but private.  

That being said you should uninstall CleanMyMac, Intego and Bitdefender according to the developer's instruction. You can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For the above mentioned software you'd do the following search(es): 

1 - Name contains cleanmymac

2 - Name contains macpaw

3 - Name contains intego

4 - Names contains virusbarrier.

5 - Name contains bitdefender

6 - Names contains contentbarrier

If you're using Tunnelblick to get to your employer's server or your bank's server or a school server keep it. If you're using it for privacy reasons you should uninstall it.

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.  

For Jack and Old Toad:

OP appears to be running something beta

System Software:

10.16.6 10.16.6 (20G5042c)

Time since boot: About 3 hours