Before she died, my grandmother couldn't remember where she'd hidden her most valuable jewellery.
She was an excellent card player 10 years before that, probably because she could recall most/all of the playing cards in the discard pile, so I'm sure she could have remembered a Bitcoin wallet passphrase — until the last few years.
I’ve unfortunately seen that as well.
Paranoia is a common side effect of dementia, and I’ve seen lots of anguish and money (legal/bank fees) spent on recovering non-life-changing savings that were just too well hidden. At least there was a fallback option to get them back – crypto would have been permanently lost.
Finding a middle ground between security and availability is hard even as a healthy adult and only gets worse with age.