Got my new '20 RST crew cab with the 5'5" bed. I previously had a '15 LTZ, and an '18 Sierra Denali with the same size beds. I had an Extang trifold tonneau that fit on both. I was told that that tonneau WOULD NOT fit the '20 RST. My salesman "threw in" a GM accessories trifold for the $500 worth of accessories he was able to "give" me. Both of my previous truck were leases, so I kept the Extang cover- just in case.
Sure enough- Last Sunday I tried the Extang out, and it fits almost perfectly! The only spot where there is even a question is at the rear of the bed. The '20's bed tapers slightly at the rear, but the old tonneau still seals completely. Needless to say, I like the Extang cover better- lifetime warranty , and will try to sell the GM accessories cover. Just a heads up for anyone wondering if their old cover will fit the new style.
NOTE- this is for the trifold soft cover, I cannot speak for the soft roll up, or trifold hard cover.