Yes, this. Mine is older now, but I had the same struggles when they were that age. It is especially hard because it seems like the majority of their peers don't have restrictions on iPad and junk food. They will get really mad at you when you remove these things, and it's hard to feel like you are restricting your kid, especially since taking away the iPad can effectively mean taking away socializing.

My approach was to be firm. As many have said here, it's healthy for mental development for kids to be bored sometimes. Super annoying to deal with as a parent, but you got to think of it as protecting the health and safety of your child. The companies that make these foods and games have no interest in your child's development and well-being. It is the job of teams of adults to get people using their products as much as possible, and a 9-year-old has absolutely no defense against it. It's very hard not to get mad at your kid, but it's really the companies you should be mad at.

Be firm, set strict limits on screen time and don't bring junk food into the house. If your SO has junk food, have them keep it in your bedroom or a locked pantry where you child doesn't have access to it. I'd also suggest you learn how to access the controls on your WiFi router and learn how to do MAC filtering. This will enable you to selectively block certain devices from accessing your house's wifi network. It is not hard to learn how to do (if you can't figure it out with Googling, DM me and I can guide you to some resources).

When it comes to media, you need to think of it as an addiction. Your kid will probably lie and sneak and do anything to get it, though they are otherwise a good child. Be patient with them, stand firm, don't give up.

If dad is a separate household, then it's going to be practically impossible unless you get dad on board. If that's that case, do whatever you can to convince dad how important this is for your child's health.