Welcome to mental illness. Many people are perfectly functional, yet still deeply sick.
I had an uncle like this. He definitely held it together okay-ish (though that's up for debate) for most of his life. But the conspiracy bullshit was a consist sign that he was not well.
And then when his wife passed, he also lost his ability to be functional, so the sickness took over entirely, eventually even took over his body. Nobody could help, not even his children.
Oh, that's awful.
My uncle also had very few allies left in this world, he was just the embodiment of an asshole to pretty much everyone. My dad and aunt were the only people that would even bother to try to communicate with him. Fortunate in some way, they'd talked on the phone the day before my uncle passed, and he agreed to let my dad stop by to drop off some food the next day. Meaning, he'd been dead less than 24 hours before my dad found his body. Otherwise, it very well could have been weeks or longer.
But the house? Total loss. My uncle had become a trash hoarder. Fueled by depression, but also by his beliefs that the government was tracking him (and would go through his trash if he were to set it outside). My dad and my cousin tried to locate some family memorabilia like photos and things, but they gave up. The house was literally bulldozed and the remnants hauled away, it was in such bad shape inside and out.