Thanos was most likely very tired, battered and overall not at his best before fighting carol. The reason I say this is because of a couple of reasons. For one he had a foursome with the Trinity
Got wombo comboed by Steve
Got his checks clapped by a bloodlusted Wanda
We even see him start to struggle with Thor a bit and being brought down to his knee
While he did one shot him with a headbutt, this should still be telling of his physically state.
Then momentarily tank the energy of the gauntlet
https://youtu.be/LMLJPDPVlUc
(2:07)
Which we already know from banner, said energy can be damaging
https://youtu.be/yzrjibEGwlg
(2:33)