If you've found your way here, it's probably because you've got a shiny new Firebeetle ESP32-E and discovered (at the time of writing this gist) that it doesn't work under Big Sur, this is thanks to the CH340 USB->SERIAL bridge not having any drivers for Big Sur.
The reason for this is that Apple has deprecated kernel extensions in Big Sur, and therefore the existing driver for the CH340 does not work and needs to be re-written to support Big Sur. A fairly lengthy gap has existed since Big Sur and now with no hint of drivers on the horizon, so you probably are going to have to use an alternative solution.
Use JTAG. If you have the JTAG pins free on the firebeetle, then with the aid of a JTAG adaptor you can use that to flash the device, and then, with the help of a different USB->SERIAL bridge (FTDI is a good bet, or silicon labs) you can tap the TX line (TTL 3.3 levels) on the firebeetle to the RX line on your serial adaptor.