Sometimes antivirus/security software (Avast, Bitdefender, Malwarebytes, Kaspersky, etc.) installs profiles or root certificates that break HTTPS after updates.
Though, we do not see any mention of the above AV or Security Software appearing in you posting
So two things come to mind
Part 1 of 2
Why another posting, specifically makes certain conclusions without any evidence to support the claim that you have AV software and that is was indeed removed
Part 2 of 2
There are 4 Categories of Third Party Software / Services that are not needed
Get rid of them via the Developers Instruction
In no special order
Third Party 2 Way Firewalls
like Lulu and Little Snitch
Commercial VPNs
They may not be what one believes they are doing for the computer and what they actually are doing behind the scenes and unbeknownst to the user ( you )
They may also reduce your Internet Speeds by upwards of 30%
https://gist.github.com/joepie91/5a9909939e6ce7d09e29
VPN: What you need to know - Apple Community
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
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
