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.