How do I find and remove AppNOS from a Mac?

I suspect you have installed adware malware.

To get a good look at your System config. for conflicts or issues, you can download/run this trusted utility https://etrecheck.com

If you need help interpreting the report you can post it here in its entirety in the "Additional Text" box in the editing toolbar below, in your reply.

You can set its preference to "Allow full Disk Access", with this you get a digest of issues from the last 7 days that are saved in your system. _No_ personal information is revealed.

If you have adware installed etrecheck will help you remove it

if not then you can yourself check fro Adware Removal Guide—

Manual removal of : http://www.thesafemac.com/arg-identification/

or

Try running this trusted utility https://www.malwarebytes.com/mac/