I recently purchased a 2020, 16-inch MBP to replace a 2008 16-inch MBP. I wanted to connect my new MBP to an external monitor (LG 27" UHD 4K, Model 27UK850). I purchased a "digipower" 7-port direct connect USB-C hub to use with the MBP. The USB hub has an HDMI out which was my preferred method of connecting to the monitor. When I initially tried to connect the monitor, it took some messing around with the connections but I eventually got the display to work and things were fine for the first two weeks. I then acquired a new, AUKEY, 10 port USB-hub to connect multiple external drives to my MBP. When I did this my LG monitor quit working and nothing I found on this thread or any other trouble-shooting sites seemed to help. I was growing very frustrated. Eventually I tried plugging in my Apple provided USB-C power cable into the USB-C port on the "digipower" adapter and the LG monitor suddenly came to life. Here is what I think is going on.
The "digipower" adapter does not receive enough power from the MBP to be able to push a strong enough HDMI video signal to the LG monitor. Once I connected the additional USB-C cable feeding power into the adapter it was then able to provide enough voltage to transmit a stable enough video signal across the HDMI cable to the LG monitor to allow it to work. I have replicated the problem several times, reliably. As soon as I disconnect the Apple USB-C power cable the LG monitor immediately dies. I believe that when I initially got the computer, my old USB hub for my external drives probably provided enough voltage to the "digipower" adapter to allow the HDMI connection to work but once I switched to the AUKEY 10-port adapter, there was not enough voltage provided to the "digipower" adapter to allow it to work.
So, my recommendation is when all these other steps fail, check your power input into whatever video adapter you are using to get the video feed into your monitor. Try plugging in either another powered USB-C or standard, powered, USB 2.0/3.0 connection and see if that won't help get your video signal to the monitor. It has fixed my issue. Good Luck!