If you see an exchange that claim to pay your transaction fees for you, you should avoid it. It will most probably be a scam exchange.
They can be either a scam exchange and try to gain more users before they run away with money by a scam exit.
Better, they don't run away with money but they will collapse by rotten management like FTX exchange. In 2020 or till 2021, FTX exchange waived out transaction fee on Ethereum blockchain for FTX users. Transaction fee on Ethereum blockchain was very expensive, $50 to $200 for one transaction in fomo times of DeFi 2.0, GameFi, Metaverse.
You can easily imagine how much money FTX wasted for their users.