virus scan app

That specific Malware / Adware scanner is one of the few I would had suggested. Notation : There are no viruses that self replicate and affect macOS. Yes, there is Adware / malware but those ere usually removed by Malwarebytes. Keep the application but no need to have it running all the time. Only launch it if there is a good reason.

NONE ! !

Effective defenses against malware and other threats

Are there any AntiVirus, Disk Cleaner, Optimizers, Defrag, VPNs etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation.