The crew at iFixit has taken apart one of the new MacBook Pros, complete with its revised keyboards. The material that makes up the membrane over the switches is new, now made of nylon, as opposed to polyacetylene on the 2018 models.
Whatever that means.
The metal dome under each key is also tweaked slightly.
Time will tell if these keyboards hold up any better than their predecessors. I think that Apple has made improvements here over the years, but the company has a long way to go before users will fully trust these machines again.