Dear Lissa,
Thanks for your updates.
I don't know why the form attachments will be added to a site list in your environment. Generally, the form attachments will be automatically saved in OneDrive for Business or a site library in SharePoint Online. Do you use the Add attachment action to add the attachments to a site list?
However, about the name change, it is by default and you can't change it. The only feasible way is to use the formula I mentioned above to extract the name part like the following and let the flow create new files in another folder.
substring(items('Apply_to_each_6')?['name'],0,indexOf(items('Apply_to_each_6')?['name'],'_'))
substring(items('Apply_to_each_6')?['name'] , indexOf(items('Apply_to_each_6')?['name'],'.'), sub(length(items('Apply_to_each_6')?['name']),indexOf(items('Apply_to_each_6')?['name'],'.')))
Welcome to share any updates at your convenience.
Thank you for your time and effort.
Sincerely
Cliff | Microsoft Community Moderator