Part 1 of 2
Download the Application Etrecheck directly from the Developer.
This is a Diagnostic Tool that makes no changes to the computer.
It makes a coherent and readable inventory of both the Hardware and Software used on the computer
The application is free or paid from added features.
The Report will Not Reveal Any Personal Information.
Post back the Full Report - copy and paste - >>>> using the Additional Text Icon ( 3rd Icon to last ) <<<<

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues
Part 2 of 2
If All the below is applicable to this computer, it would show up in the report anyways .
Any Third Party Applications that will interfere with the normal operation of the OS, is an invitation for disaster and comprising the Operating System
Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale. What the Application may do to the computer is up to the User to check this out before purchase
Any of the below should be removed as per Developers Instructions
1 - Disk Cleaner
This will include CleanMyMac , aka “ BrickMyMac “
MacKeeper,
Dr Cleaner Pro Plus
Open Cleaner one Pro
Macmechanic
2 - Third Party Security Software
This will include BitDefender ,
This will included Norton Antivirus
Sophos Av Software
Intego AntiVirus
McAfee,
Avast AntiVirus
Ad Guard,
Webroot ,
ESET ,
Avira ,
AVG AntiVirus
avira antivirus
Trustee
AntiVirus for Mac
F-Secure
Securemac
Cylance
Read some of the posting and arrive at your own conclusions.
The The Built in Security is all that is required.