Step 3 - I didn't know about the cogwheel, nice!
Step 4 - fan did not start
Step 5 - local time looks good
Step 7 -   Operating System: Debian GNU/Linux 11 (bullseye)
           Kernel: Linux 5.15.84-v8+
           Architecture: arm64
Step 8 - after reboot:
           Operating System: Debian GNU/Linux 11 (bullseye)
           Kernel: Linux 6.1.21-v8+
           Architecture: arm64
Step 9 - git version 2.30.2
Step 9.1
    Name: pyserial
    Version: 3.5
    Summary: Python Serial Port Extension
    Home-page: https://github.com/pyserial/pyserial
    Author: Chris Liechti
    Author-email: cliechti@gmx.net
    License: BSD
    Location: /usr/local/lib/python3.9/dist-packages
Step 10 - The script reboots the device
Step 10.1 - After reboot, the fan is not running
    Service is not working:
	umbrel@umbrel-test:~ $ sudo systemctl status deskpi.service
		● deskpi.service - DeskPi Fan Control Service
			 Loaded: loaded (/lib/systemd/system/deskpi.service; enabled; vendor preset: enabled)
			 Active: activating (start) since Mon 2023-05-01 19:05:48 MST; 47s ago
		   Main PID: 837 (pwmFanControl64)
			  Tasks: 1 (limit: 8755)
				CPU: 15ms
			 CGroup: /system.slice/deskpi.service
					 └─837 /usr/bin/pwmFanControl64 &

		May 01 19:05:48 umbrel-test systemd[1]: Starting DeskPi Fan Control Service...
	umbrel@umbrel-test:~ $ sudo systemctl start deskpi.service
	[HANGS...]
Step 11 - Everything is ok except I need
   chmod +x /home/umbrel/deskpi/drivers/python/*.py
Step 11.7 - fail
	umbrel@umbrel-test:~ $ sudo systemctl status deskpi.service
	● deskpi.service - DeskPi Fan Control Service
		 Loaded: loaded (/lib/systemd/system/deskpi.service; enabled; vendor preset: enabled)
		 Active: failed (Result: exit-code) since Mon 2023-05-01 19:18:09 MST; 45s ago
		Process: 639 ExecStart=/usr/bin/pwmFanControl64-v0.py & (code=exited, status=203/EXEC)
	   Main PID: 639 (code=exited, status=203/EXEC)
			CPU: 1ms

	May 01 19:18:09 umbrel-test systemd[639]: deskpi.service: Failed to locate executable /usr/bin/pwmFanContro>
	May 01 19:18:09 umbrel-test systemd[1]: Started DeskPi Fan Control Service.
	May 01 19:18:09 umbrel-test systemd[639]: deskpi.service: Failed at step EXEC spawning /usr/bin/pwmFanContr>
	May 01 19:18:09 umbrel-test systemd[1]: deskpi.service: Main process exited, code=exited, status=203/EXEC
	May 01 19:18:09 umbrel-test systemd[1]: deskpi.service: Failed with result 'exit-code'.

Running the file directly:
	umbrel@umbrel-test:~/deskpi/drivers/python $ python3 /usr/bin/pwmControlFan-v0.py 
	Traceback (most recent call last):
	  File "/usr/local/lib/python3.9/dist-packages/serial/serialposix.py", line 322, in open
		self.fd = os.open(self.portstr, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
	FileNotFoundError: [Errno 2] No such file or directory: '/dev/ttyUSB0'

	During handling of the above exception, another exception occurred:

	Traceback (most recent call last):
	  File "/usr/bin/pwmControlFan-v0.py", line 31, in openSerPort
		serPort = serial.Serial("/dev/ttyUSB0", 9600, timeout=30) #Open the serial port (ttyUSB0). Deskpi uses it to communicate with the Deskpi Pro fan.
	  File "/usr/local/lib/python3.9/dist-packages/serial/serialutil.py", line 244, in __init__
		self.open()
	  File "/usr/local/lib/python3.9/dist-packages/serial/serialposix.py", line 325, in open
		raise SerialException(msg.errno, "could not open port {}: {}".format(self._port, msg))
	serial.serialutil.SerialException: [Errno 2] could not open port /dev/ttyUSB0: [Errno 2] No such file or directory: '/dev/ttyUSB0'

	During handling of the above exception, another exception occurred:


I checked /boot/config.txt for the magic line.  It is there.
/dev/ttyUSB0 does not exist.