It's been hard for me, but I've got physical spaces in my home (helps to have a house for this) that I use for different things. Upstairs loft (which will be a space for kids later) is my office right now. Living room is time with my wife, sitting room is my reading room. If I take a book to the sitting room, I can actually read it and get something done. I usually leave my phone in another room.

Another thing that used to work really well (recovering from a pulled muscle so I can't presently) is to leave the office and go for a run. With WFH, I started doing that again 3 days a week after work, another day was lawn work. It's not something you can choose to focus on or not, you're out there and have nothing else to do but move. It creates a clean separation between my workday and the rest of my day.