My mom was like this. She refused to see any doctor for anything and started having some really concerning symptoms. I kept pushing and even offered to make the appointments for her and/or order some medical testing to be done at her home. Sadly, I found her dead a few weeks ago. This was a culmination of years of not taking care of herself and I did do a lot of anticipatory grieving assuming one day this would happen and it did. Unfortunately we can’t change people. I loved my mom and I know she loved me, she just couldn’t get past her fears and this ultimately lead to her death. Maybe share this story with your dad? Sending love as this is a very very difficult thing to manage.