In Assistive Access mode? What version are you on?

My dad passed in the spring, so it's moot for me, but I'd be glad to know that they've fixed it for other people.

[Edit: someone else in this thread said it's still bugged in 18.6.2, so if you've got a working build it'll be particularly helpful to know which it is. Maybe even for Apple - I maintain a fond delusion that folks who matter still read this board.]

Oh, I didn’t realize AA mode was required to break the feature. Have 15.8 and very recent versions.

Sorry, I may not have explained the problem well. Yes, in AA mode, the screen is always unlocked, regardless of any device settings you may otherwise, er, set.