First, this is what happens:

I have been told that the "real" path is "/home/pi/PandaPI/Marlin2.x/pandapi/stm32f103cbt6.bin" but I do not understand why they look different. I have, however confirmed that this path exists and the bin file is there.
I was also told that "one jumper" needs to be installed in order to accomplish the MCU flashing, but I have not been able to guess which jumper that is.
It is, of course, essential to be able to reflash the MCU and the Pandapi can not be installed until that is confirmed. It would be really nice if it could be done with a bootloader instead of a hardware programmer.
Does anyone know what's up?
This issue needs a guide.
the v2.8 2021/3 and later version has bootloader,
configure the hardware with jumpers and line,the yellow line is used for connect the reset pin of MCU to PI,so PI can restart the MCU before flashing.
I don't have a solution, but am reaching out again for a solution to the same problem.
I get the same message, but I have v. 2.5 PandaPi board. The firmware is 2.0.8 and is compiled.
Can a v.2.5 board update the MCU? The touchscreen still thinks it's at 2.0.6, and it knows none of my Contact information.
Also, to be clear, I am sure that the MCU DOES NOT need updating. I simply need to know HOW to do it for the future.
It is the most recent version - 2.8. The image I used was the most recent Pi4 image - PandaPi4_20210320.img
wich PandaPi Version exactly you have and wich image did you use?
usually it should be enough to click 'Run Marlin' then 'compile' and then 'run'