Internet browsing problems that worsen over time until nothing loads.

OP wrote " It is a business system, and it does have Sophos AV installed as well as the Fortinet VPN Client./

Obviously, the Companies IT Department knows a lot about Microsoft Windows Environments but has very little actual knowledge / experience when it comes to macOS on Apple Computers

There are 4 Categories of Third Party Software / Services that are baffling.

In no special order 

1 - Third Party 2 Way Firewalls 

like Lulu and Little Snitch 

2 - Commercial VPNs 

They may not be what one believes they are doing for the computer and what they actually are doing behind the scenes They may also reduce you Internet Speeds by upwards of 30% 

https://gist.github.com/joepie91/5a9909939e6ce7d09e29

VPN: What you need to know - Apple Community

3 - Third Party Security Software 

There are no known Windows-like Viruses in the wild that self replicate and affect macOS, because of the underling UNIX  Foundation and Permission Limitation. 

The Operating System resides in a Sealed and Read Only Volume that cannot be opened by the User nor by Third Party Applications.

The Only thing this Antivirus software is protecting is the Bank Account of the Developers and for zero return to the User aside from the problems this software creates.

Security. Built right in

Mac app security enhancements

The Built in Security  is all that is required to protect the computer.

Protecting against malware in macOS

4 - Third Party Disk Cleaners / Optimizer 

Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster. 

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a percentage on each sale. 

What the Application may do to the computer is up to the User to check this out before purchase

To put the Third Party Disk Cleaner / Optimizer in context and the damages it may have or has already done.

This type of applications can or will Muck Up your User Account ( Home Folder ) of this machine.

It does not touch the Operating System itself unless you consider your User Account ( Home Folder ) as part of the Operating System.

The Operating System is hosed

By far the easiest way to cause poor performance, instability, overheating and crashing is to install ANY third-party speeder-uppers, Cleaners, Optimizers, or Virus scanners, Bit Torrent, or a VPN that you installed yourself.

¿Do you have anything like that installed?

For what it's worth, having Sophos AV and Fortinet VPN Client installed is a certain road to problems. If you are going to keep them installed, check with their vendors to see if they have updates for Tahoe.

Grant Bennet-Alder wrote:

Owl-53--

Your writing above looks like the heart of a User Tip.

If you ever find yourself needing to post the same information again, consider making it into a User Tip.

+ 1

Thank you

User Trips, I may take that under conservations

Owl-53--

Your writing above looks like the heart of a User Tip.

If you ever find yourself needing to post the same information again, consider making it into a User Tip.