Here's screenshots of the basic process

1) I call the flow from a Power App and pass in the name of the column, the list, and the item ID
2) I create a variable with some base HTML to hold the comments
3) I use a REST call to retrieve all the previous versions of the item.

4) I Parse the output of the REST call to access the individual versions and columns in the versions
5) I loop through the versions and append the results of the specific column to the string variable. I include the date/time when it was made and the author with the comment
6) I return the string variable to the Power App where it is displayed in a Rich Text field.
I hope that helps.
One thing I learned since I made this example is that inside the loop you should check to make sure this revision contains something in the column. If people edit other things in the item it will create a new revision, but there won't be appended text. That check isn't in this demo.