When I purchased my Cannondale SuperX, the shop told me they've never seen a carbon bike come in with damage caused by a trainer. They also said trainers were considered "normal use" by Cannondale and covered by their frame warranty . The only concern they had was that I not over-tighten or strip/cross-thread the thru axles. Those concerns applied equally to non-trainer use as well.
I do know that some (not all) manufacturers specifically state that trainer use voids warranty, but some also specifically state that their bikes are fine to use on trainers. Canyon, for instance, has this:
https://www.canyon.com/en-ae/support...o-trainer.html and they even go so far as to say bikes not on their "approved" list are still fine for use on trainers, but they just haven't specifically tested them for this type of use. Canyon will also offer crash replacement for trainer damage on any bike, even if it's not specifically on the list.
While googling the topic, I found this article which also seems to concur that carbon frame damage from trainers is a myth, though it may still void your warranty depending on which manufacturer you're dealing with:
https://zwiftinsider.com/will-indoor...-carbon-frame/