Hate to say it but I have this problem, too. Chrome just freezes up and you can't do anything. Can't press the back button. Can't press the home button. Can't press anything. And then about 10 or 15 seconds later it will kick you back out to the homepage (most likely because you've pressed the back/home button so many times in frustration).
I have no clue where the problem originates, if it's chrome or the S20 Ultra or what... but I can confirm that Chrome is definitely freezing on the Galaxy S20 Ultra. Unfortunately it cannot be easily reproduced and seems to happen at random times.