Had a similar problem with a Pi 3B.  Ended up buying one of these to boost its signal.  Works okay with this.

https://www.amazon.com/gp/product/B07M7V5LKZ/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1

Bit of a pain for portable use as it's another device to tote, plus extra HDMI cable, etc.  Does fine at home.

GL

Chuck

KD9DVB

On Tuesday, June 23, 2020, 2:33:57 PM EDT, w9ran <w9ran@...> wrote:

Hopefully this isn't your issue, but I recently found one of my Pi 3Bs
would no longer display hdmi output even though it has for months.   A
different Pi worked fine on the same monitor and cable.   Since ssh was
enabled I was able to communicate with it and tried all the stuff you
find in the FAQs, knowing it wasn't just a config.txt setting because
there was no video at startup which comes from the bootloader not from
Linux.   Google searching confirmed that random hdmi hardware failure on
the Pi is not unheard of.   Since the composite video works and the
published documentation doesn't show anything beyond the hdmi connector
I'm not optimistic about being able to fix it, but am open to suggestions.

73, Bob W9RAN