On reset, the ESP8266 will print bootloader messages at 74880 baud. Since you have set the monitor to 115200 baud, the USB-UART adapter cannot correctly the UART TX signal and prints the wrong data. What is being output at minotor_speed = 74880? I suspect your ESP just can’t boot.
I see that you’re using a Mac by that /dev/cu.usbserial* device name. Serial drivers for like CH340 chips are known to be very buggy / needing the exact right kernel driver. See Troubleshooting CH340G issues on macOS. If no sensible output is shown on any baud rate, a driver issue may be fault.