I had this exact same problem. After having to replace the screen on my 2020 MacBook Pro 13" having thrown coffee over it, it wouldn't power on. However, I researched and found this article. It turned out that ribbon cable had broken, presumably internally, and when I flipped the compression latch up on the larger of the two ends, it somehow let go and launched itself into orbit never to be seen again! I ordered a new cable from Germany along with some Kapton tape. I shimmed the end of the ribbon cable with two pieces of Kapton tape and using tweezers, persuaded the cable into the connector (okay, I admit the wrong way up first time, second time lucky!) At this point I turned the laptop over and powered on.....nothing. I did wonder if the battery had run flat, unlikely but not impossible, so I connected the power cable and of course it powered up. The difference this time was a battery icon on the display whereas before there was no icon and the display was multicoloured flashes and full speed fans etc....