Hi @grahamr,
If you want to get history comments, you should get history versions. You could use Send HTTP request to SharePoint to get these versions of the file or item.
The URI is:
_api/web/lists/getbytitle('List')/items(itemID)/versions

Then you could initialize an array variable to hold these comments.
The following expression means to get the array of versions:
body('Send_an_HTTP_request_to_SharePoint')?['d']['results']
Then put the array into apply to each action to loop through each version, append their comments into the Comments array variable:

This is the code in the Value field:
{
"comments": "@item()?['OData__x005f_ModerationComments']"
}
After all, you could convert the comments variable into an HTML table to make it could be inserted into the EMail body:
Best Regards,
Community Support Team _ Lin Tu
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.