Noting for updating of Firmware Uploader documentation:
The README indicated the original Ender 3, and "possibly other Creality printers", required flashing of a bootloader--I'm happy to say that this is probably an issue restricted to the original Ender 3.
Personally own a CR-20 Pro (which uses a different motherboard, but otherwise is essentially an Ender-3 mechanically but with some extras like incorporated BLTouch), and can confirm a successful flash of Marlin firmware 2.0.9.5 on this, using instructions in the Creality community for flashing other CR-series printers which use an ATmega2560 processor. In our case, it required setting avrdude to "wiring" rather than "arduino", but got a successful flash out of it.
Very likely it's only the Creality models that use an ATMega1280 that are affected by a lack of bootloader, and potentially just the Ender3 original (it may not even apply to the various iterations and upgrades).