If add_theme_support('amp', [ 'paired' => true ]) is present, then a user should still be able to still switch from Transitional to Native via the AMP admin screen, and back from Native to Transitional. If a site works in Transitional mode then by definition it should work in Native mode. But if paired => false (or paired is absent), then Native would be the only option, as the reverse is not true: if a theme only works in Native mode then it may be using AMP components in its templates (e.g. amp-sidebar) without any non-AMP version also implemented.

This will allow all Paired themes (e.g. Neve) to be also used in Native mode.