Why can’t I turn on battery percentage on my iPhone 11

As shown in the support document you posted from, the feature is not supported on iPhone 11. Apple has not said why this is, but it's likely to due to screen size, which would make the percentage text which appears inside the battery icon on other models incredibly small and as such very hard to actually read.

That’s so dumb, it offers it to iPhone 11 Pro but not the 11-

If you update to iOS 16.1 you should be able to turn it on.