Malware Blocked Pop-up window

Post the free EtreCheck report using the Additional Text option when posting and it will identify the files in the Launch Folders. The report contains no personal information. While this is not an alternative to the clean install you are planning and recommended, it will identify the problematic app.

How to use the Add Text Feature When Post… - Apple Community

False e positive by Avast anti-virus scanner.

Once this type of software are installed and embedded into the computer " Avast anti-virus scanner. "

Start Over from Scratch 

Heavy Handed - Yes ?

Effective in removing the AV Software - Yes 

You can spend hours or days hunting down all the bits and pieces of this software and never really get it all off the computer

For Apple Silicon computer >> Use Disk Utility to erase a Mac with Apple silicon.

For Apple Intel computers >>   Use Disk Utility to erase an Intel-based Mac followed by How to reinstall macOS

Always make a Time Machine Backup  before  proceeding 

If going this route - I suggest Not using Startup Assist to migrate everything back.

This will probably Re-Introduce ( Avast anti-virus scanner ) back into the Operating System 

AnyAssistantsIsAppreciated wrote:

My last resort to is to do a time machine backup to a external HD and then factory reset the new silicon based macbook air. Then install my apps and data slowly (when needed) from the external HD back to the new silicon based macbook air. It will be time consuming but I hope that may pin point the issue.

That is always the best option for migration, especially a big change like Intel to Apple Silicon.

There are some methods that will identify the specific files more quickly and easily, but I can't mention them here in the forums as it may result in compensation, financial or otherwise.

I suspect the problem app is Citrix, do not install it after doing the clean install.

AV software whether migrate from old to new or installed freshly only on new

The issue remains the same Full Stop