Will I brick my Ender 3 if I try flashing without a bootloader? I have a recently purchased Ender 3 Pro, and it may well already have a bootloader on it. I don't have the various adapters to flash one yet.
Is it destructive to try flashing over USB without the bootloader? Does it fail in a non destructive way?
I have watch some tutorials which claim that it's fine to just try it, but I'd like to be more sure about that.
My understanding is that if there is no bootloader, you can't flash over USB; you need an ISP programmer attached to the board. So if you're able to flash over USB, that means there is a bootloader, and updating via the bootloader should leave the bootloader in place and just overwrite the rest of the firmware. I'm not sure how strongly this is enforced, though, so you may want to wait for supporting comments/answers from others.
Of course it's always possible to damage your printer in ways that require replacement of the board or at least some parts on it if you flash bad firmware, so you need to be cautious anyway.