How long did you leave on? It often needs to be overnight. And make sure it is on tight enough to keep the power button pressed. You may have done all that but wasn't clear with the details you provided.
If you are on Stock, you do have a recovery. When you get the dead robot you need one more step. (This link is about the Pro 1, but I believe it is the same for the Pro1x-- not that I can test being on LOS 21) Whether getting to recovery helps or not, I don't know, but there is a stock recovery already.
Another DOA phone that wouldn't charge here. I was relieved to find this forum and that I was not the first to have experienced the problem.
And I am happy to confirm that the rubber band hack worked for me also...
Phone was still unresponsive after six hours, but the following day (after a total of 18 hours) it sprang to life.
DigbyT