Text in labels and other controls is not selectable (unfortunately), in this regard egui behaves as a native app, so mostly just editable texts are selectable. This feels a bit unnatural on the web, but one must consider that egui uses a custom WebGL renderes, so the content is not backed by standard DOM.

On native apps with Qt text on any widget can be made selectable via a property.

The text in the textbox is selectable, so it's not like egui can't handle text selection. It's just following convention with making GUI text unselectable.

Non-copyable texts by default in "native" applications sounds reasonable but is actually one of those things that introduces unnecessary friction down the line when users try to write tutorials or reports and have to manually type out everything.

Yeah, I would like to see that behavior as an option, or even better allow to select the whole UI as a block of text (to feel natural and be searchable on the web). I belive any UI (incl. native) should not prevent you from copying any text.

Yeah, it's not using the dom, it's using a canvas with webgl.