We asked Samsung how it offered an IP68 rating and a user-replaceable battery, and the brand told us that it did so by having seals at different places.
It offered both because it chose to do so. I don’t understand this collective amnesia people have about replaceable batteries and waterproofing. The Galaxy S5, released over 10 years ago, had a replaceable battery and an IP rating of 67. The only reason we don’t have this on modern smartphones is because manufacturers realised it was more profitable to seal the battery inside the phone and force customers to pay for a repair or an entirely new phone. There is no design black magic going on here; the company just knows a replaceable battery will improve sales for this niche model.