What it looks like, why the misread happens, and what changes the outcome when someone in front of you can't follow your instructions.
Notice what you've already concluded. By the time you're out of the vehicle you've usually read the situation, and that read came fast, off experience that has mostly served you well. This is the narrow category where the fast read is wrong, and one breath before you act on it is the whole difference.
Sudden confusion that came on over hours, one-sided weakness, a drooping face, slurred speech alongside those signs, or a head strike point to a stroke or an injury, and none of what follows applies until that's been excluded. Low blood sugar presents the same way and is just as fast-moving. Check that before you check anything else.
Past that, dementia symptoms overlap almost exactly with the things you're trained to recognize as intoxication or defiance. Impaired coordination, slowed or slurred speech, disorientation to time and place, emotional volatility, repeating the same thing over and over. That's also the intoxication checklist. The overlap is close enough that the misread is the expected outcome, not a lapse in attention, and it's common enough that officers in one study reported routinely mistaking people with dementia for homeless or intoxicated individuals rather than someone in need of help.
If de-escalation isn't reducing risk, that judgment is yours and this page doesn't displace it. What changes is what you're carrying into the decision. Force applied to someone who is frightened and can't process instructions tends to confirm the threat rather than end it. Where your protocols allow the extra minute, the extra minute is usually the faster route.
Almost none of what goes wrong on these calls goes wrong during the struggle. It goes wrong in the four seconds before, when confusion gets filed as defiance.