If your loved one has shadowing really bad, how hard will it be for them when they go into a NH?

I think your husband will do better in a NH as the structure is different. There are other people/activities that can provide a different focus. I think that being the PC at home creates an environment for the shadowing. I can understand your situation as it is similar to mine. Younger onset, husband is 58yo and in stage 5, diagnosed in 2020 but signs were there much longer, at least 6 years. His shadowing is mostly when I am in the kitchen so related to food, but is starting to get worse during the afternoon/evening. Take care of you now.

Never allow a shadowing habit to establish itself. It's hard to prevent and sometimes a caregiver has to be a little tough to make sure it doesn't.
I could never tolerate this behavior because I have never allowed a client to ever establish a shadowing habit with me. How you stayed on such a job for years is beyond me. You did not leave on your days off?
I had a position years ago that was a four days on, three days off live-in. It was the only live-in assignment I ever took because I do not take live-in work. The money was so good and the accommodations were very nice.
I knew an old-school CNA who at that time was my age today. She warned me about letting a shadowing habit form and how to prevent it. I did what she said and stayed on that job about a year. I didn't like living at work so I left.
The other aide who did the other three days in the week, was going crazy because the client wouldn't leave her alone. She had to move a couch into the client's room and sleep there because the shadowing was so bad. She had to keep a chair outside the bathroom door so the client could be there while she used the toilet. The client had to be in the bathroom while she showered. She would get hysterical, cry, shake, and hyperventilate if she wasn't. I didn't have this problem with her.
The family put a gate in front of her bedroom door so she couldn't wander at night. Her room was secured as was the rest of the house. I checked on her twice a night to toilet her if needed. That was it. The other aide was going in there every five minutes all night long. Not me. Bedtime was 8pm. I made sure she had a snack and a drink in her room, then I'm off duty until it's toileting time. If I needed to get something done or needed a break from her for a little while during the day, I'd put her in her room with a snack and the tv on. She'd yell, cry, command, swear and threaten which i would just ignore. This went on for about a month then stopped. She got used to me coming in only twice a night to bring her to the bathroom. She got used to watching tv in her room during the day at times. Never allow a shadowing habit to establish itself.

Thanks, your answers makes me feel better.