Part 1 of 2
I second what my colleague has outlined + 1
Windows-like viruses that self-replicate and affect macOS don’t exist because of the underlying UNIX Foundation and permission limitations.
The macOS operating system resides in a sealed and read-only volume that can’t be opened by users or third-party applications.
Mac app security enhancements are sufficient to protect computers from malware.
Adware and Malware can affect computers and are often downloaded from “shady” websites or developers who inject them into downloads.
Source: User tip from @Kurt Lang
What is malware? - Apple Community
Part 2 of 2
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
Disk Cleaner
CleanMyMac , aka “ BrickMyMac “
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