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Is it possible to get a list of files that so not contain the specific string of characters

Thanks

Yes. It's possible to do with AFR.

Go to Find tab.
Check Native type.
Then enter a string with minus (-) sign before it.
For example,
-"hello world"
Will search for files that do NOT contain hello world as a string.

or you can use -hello (without double quotes) to search for files that do not contain hello.