How to apply $regexMatch to an object field that's nested inside an object with the MongoDB Aggregation pipeline?

Question

Is there a way I can build an aggregation pipeline stage to do a $regexMatch on an object field nested within another object. I typically see examples using the $addFields aggregation pipeline stage, so I've been trying to do a match with this stage. I'm trying to do a search on the word word within the string_text field of each object.

Note: This needs to be done in the domain file when building the aggregation pipeline.

Here is an example of the data I'm trying to do a $regexMatch on, in this case the text field:

{
    array_of_data: [
        textObjects: {
            text1: {
                string_text: "Matching word here"      
            },
            text2: {
                string_text: "Looking for the matching word which is here"     
            },
            text3: {
                string_text: "Won't find it here"    
            }
        }
    ]
}

I've been trying to build it solve this issue with a $filter operation, but still don't get the results I'm looking for, it returns every document and not the ones with the word word in the string_text field.

Any help would be appreciated, I've been struggling with this for a few days now :(