Search Engine Malware on MacBook Air 2015 - Find and Delete .plists

First, start your Mac in "Safe Mode": How to use safe mode on your Mac - Apple Support. Starting in Safe Mode takes longer than usual so let it finish.

While in that mode, drag these files to the Trash:

First screenshot:

Second screenshot:

Third screenshot:

Then, restart your Mac normally and confirm the alert messages cease to appear.

Note: Non-Apple "drive manager" or "utility" products are not required on Macs. Western Digital's product in particular was notorious for spontaneously erasing perfectly good hard disk drives in the past. Although it is not related to the problem at hand I recommend uninstalling it for those reasons.

Yes. All of them should be dragged to the Trash. You may need to do that in "Safe Mode" as well.

Those things are all installed through deception. For a somewhat outdated but still relevant description of how that happens, read How to install adware - Apple Community.

People can't seem to resist installing free stuff, even if its Terms and Conditions make it abundantly clear what it's going to do — which is in essence to mess up their Mac and make it do things no reasonable person would want.

Interestingly, I have never encountered a single piece of Mac malware that does not do exactly what it says it's going to do.

Upload those screenshots here.

For detailed and illustrated instructions, read Removing "Search Marquis" / "Search Baron" / etc on your own - Apple Community.

You're welcome. Glad to help.

Seems your friend has a momentary lapse of judgement around the end of 2020 / beginning 2021. It's ok. The whole world did.