Does not happen in 1.16.5. In the Create New World screen, if the game mode is Survival, and the world type selected is Debug Mode, the game mode button displays "Survival", even though it states below that "you can look but don't touch", which is the help string for spectator mode. Same case with "Hardcore" and "Creative".

How to reproduce:

1. Click "Singleplayer".
2. Click "Create New World".
3. Click "More World Options...".
4. With any Alt key held down, click "World Type" until it displays "Debug Mode".
5. Click "Done".
6. Look at the "Game Mode" button.