MRT.app Infection

I would suspect that AVG is giving you a "false positive" about MRT. macOS security hinges around a number of components, including: A definition file, called: XProtect, an automatic definition file updater, and a temporary system scanner, called: MRT. (Maybe stands for Malware Removal Tool?) MRT will scan your Mac for known malware and notify you that any malware detected has been removed. The scanning process should only take a few minutes, but it is possible that it can become "stuck."

I do not recommend removing MRT. Each subsequent Apple security updates will update each of these components and I would suggest that you apply them as they become available. What I would recommend is completely removing AVG as it is not needed and any AV app can cause more issues than they resolve.

The item Avast flagged is part of the OS' security system. It's supposed to be there. MRT is short for Malware Removal Tool.

Get rid of Avast and any other such junk you've installed. There is no AV software that is worth one cent of your time or money on a Mac. They do nothing useful. They do, however, excel at wasting system resources.

Be careful as this is a virus which can replicate itself, into different files, so be mindful with any changes you make and ignore

Where did you find that information? We would all like to know as there currently are NO viruses for a Mac.