I used to think that the bootloader is in the non-erasable part of the memory and it is possible to load the oem program via UART. However, if I am wrong , would that mean that I am unable to do anything without JTAG?

I am solving exactly the same problem on a board where I have SoC ESP32 d3. I assume that after delivery from the vendor, there is a pre-burned bootloader in the processor to load the oem_firmware. However, after turning on the terminal I see the same output as in the previous post. --- WARNING: GDB...