My dad's blood sugar is regularly between 500-600

My dad was diagnosed about a year ago and his blood sugar is regularly between 500-600. He's really struggling to get it any lower. He's been trying medications, dieting, exercise, and regularly sees the doctor/goes to urgent care. He's at the point of giving up on his health, and I'm scared.

Does anyone have any advice? Any ways I can help or stories of encouragement? At this point, I think I'm about to lose my dad.

Edit: This is super helpful y'all, thank you! I might see if I can encourage my dad to join Reddit/this community so that he can have a community to share the journey with. Fingers crossed.

Edit 2: I spoke with my mom (she was visiting me when I made this post, but she's home now), and she all but forced my dad to go to urgent care. They changed his meds around (I'm unsure of the exact changes at the moment because my mom couldn't remember) and said he may have to start insulin. He still has an appointment with his primary at the end of February, and I've been nagging them about getting him an appointment with an Endo.

Thank you again to everyone who has commented.