[SOLVED] 9.01 does not start

[Venerdi]

I don't see anything suspicious in the log. 

Try turning the Display off/on, re-seat the HDMI cable and then reboot the Pi.

@Tim

I solved the display problem, I made a change, using intuition (or unconsciousness, since I don't understand anything about it).
The point is that I made this change by viewing old backups where everything seemed to work and studying the differences with that of 9.01, everything was resolved, but I absolutely don't know what the changes I made mean.
I changed these two lines from the config.txt file
dtoverlay=vc4-kms-v3d
max_framebuffers=2
with
#dtoverlay=vc4-kms-v3d
#max_framebuffers=2
I disabled them.
Now I wonder... what did I do? Why does everything work now? What do those two lines mean? Booting is also faster.
v.