I use the same Hirobel others have mentioned on my Trek Domane carbo bike. On my work stand I would normally clamp to the top tube before I had a carbon bike.
I have a Jamis Renegade steel gravel bike that has a carbon seat post. I just had that seat post fracture while riding, after under 2k miles of riding. Jamis replaced it for free, and I had never clamped onto it or exceeded the torque spec on the seat post clamp, but I definitely recommend not assuming weakening a carbon seat post is not a big deal!