Where can I find a suggested/example/template letter of incompetency for a physician to use?

I've searched the forum and can't find anything specific. My parents were diagnosed with MCI a few years ago and are now in full cognitive decline. When they were capable and competent, they had the foresight to create a POA granting me full medical, legal, and financial power in the event they become incompetent or incapable. Now, my elder care attorney tells me that to "activate" the POA's, I need a letter from their physician stating that they are no longer capable of making financial decisions or legal agreements. This is not guardianship, just activating the POA's. Their physician only has experience with guardianship and doesn't have a form or template for a letter of incompetency. I found other posts here stating the same - no physician form or template for incompetency letter. I did find one post that said it is state-specific and tried to post a link to a CA state form but the link failed. I've found a few examples on the web but they are not specific to TX. Has anybody else tried to do this? Any suggestions? Thanks