They're screwed unless they update. Luckily the iPhone 6 was still getting security updates as of this year. It doesn't have ios 13+ but it does have security updates on 12.

As a 6 user for another month or so, my biggest complaint isn't slowness, it's the lack of ram that causes apps to be closed readily whenever you switch, compounded by the apps having to boot/reload again.

Most of the apps I use aren't IOS apps, they're things like chrome.

This is nothing like using a 3g or a 4 until they stopped getting updates, those were downright painful to use. This is merely frustrating.

I don't know what people expect from their phones, but 5-6 years of updates and the phone still running well is incredible. I hope my next iPhone gets me another 6 years. It seems likely.

I don't know what it's like in Android land, but I expect that the number people using a phone at all for 6 years is even less than those using old iPhones. At least they had way more ram for a same era phone.