The bug
After installing Minecraft using the installer on a PC where Minecraft has never been installed before, the snapshots profile is selected by default without any user interaction.
Especially for new users this can cause issues because they might not know that snapshots are experimental.
How to reproduce
Perform a clean install of Minecraft
Note: It appears deleting .minecraft/launcher_profiles.json
before starting the launcher is not enough (?).
This has already been reported in MCL-12075