Should I help my elderly dad with a melanoma brain tumor with something? That makes me feel uncomfortable, and maybe unsafe for him.

What kind of platform?

If he is planning on dropping off the platform, to not die of his brain tumor, he is putting you at risk of criminal charges.

I used a gait belt and was trained to do it by my LO's PT. Even after training, it's a bit dicey. They can lurch in any direction, and I never felt confident that I could save LO from disaster if the worst scenario happened, which would be falling in a way that I couldn't control. Until they do that, you haven't had any practice in yanking them up. You don't know how to maneuver them back to safety.

It's different for professional caregivers. They've had long experience, and the patient is safer with them.

It's best not to get involved in this with your father, IMO. If you mess up, consequences could be dire. Then he could blame you for that.

In your profile you say you suffer from stage 5 kidney disease and have no experience with elder care. Please do not use a gait belt to help dad step outside because he can easily fall and take you down with him. Then what? If dad decides to go outside on his own and falls, call 911 to attend to him. Trying to lift him up in your condition is a bad idea.

Melanoma cancer is likely in other parts of dad's body if it's gone to his brain. Does his doctor recommend in home hospice to keep him relaxed and comfortable? You may want to ask about that.

Best of luck to you

My guess is that F has heard or read something about a gait belt, and thinks it will work for him. Tell him that you understand it requires a lot of strength and training about how to use it. You will find out about the training, and let him know what the trainers say. It’s a different way to say NO.

I believe what you're referring to is what is called a gait belt. They are not all that easy to use, and one really needs to be trained in the proper way to use them so you don't hurt yourself or the one you're trying to lift.
So the simple answer to your question is no, you should not do anything to help your dad if you're not comfortable doing so or if you may get hurt.
It may be time that your dad gets placed in the appropriate facility, where you can just be his advocate and child again, and he can receive the care that he now requires.

No. It isn't safe to do. At least in so far as I can tell from the few details you give us. As you note, your father's brain is not functioning normally. And as you say, you understand his responses are not always appropriate. My concern here is whether or not your father will determine to do such a thing without your help.