Any ESP32, RP2040 or RP2350 board. The last two use external QSPI flash, so hobby projects only. There are no fuses to set to read protect the firmware.

Just to be clear, some micros (STM32s come to mind) have what they call "on the fly decryption" for external flash. Basically, if the micros wanted to, they would. I think ESP32s are also using qspi flashes but they're integrated in package? Maybe that's changed but that's how I vaguely remember it