Dear Michael,
As the automatic flow has no folder connector action in SharePoint Online, the easiest way I suggest you is to use a list trigger as a workaround.
First create a list naming List for selected folder (for example) and create a folder content type in the site naming Folder for list 1 via the detailed steps in the article. Then add a column in the list List for selected folder naming Users who select the folder. Click on New to add a folder for the list with the folder content type>click on Edit form to enable the hidden Title column for the folder and add files as attachments in the folder.
The flow is created as follows.
Trigger the flow: When a new item in the list is modified. You can let users fill the values in the column Users who select the folder when selecting the folder in the list to trigger the flow.
Then the flow will get the attachments of the folder in the list to send an email with attachments automatically. You can also not use the folder and just use the list item with attachments as well.
However, if you want to trigger the flow in the folder in a library, you may write some custom expressions.
Here is an thread for your reference.
Best Regards,
Cliff