You are focusing on the wrong item. Throughout the last posts, you have been looking at the communication between Klipper and OctoPrint, which is irrelevant for your case.
What is not working is the communication between the printer board and Klipper. (For the last time), I’ll direct you to Issues flashing the printer board, as the solution is almost certainly among the listed items.
The relevant error lines are only visible in the klippy.log, for example:
serialhdl.error: mcu 'mcu': Serial connection closed
As long as you have these lines in your log, you don’t even need to bother looking into or using OctoPrint.