For personal or non-deceptive use, removing the Gemini watermark is generally fine. Google’s terms give you broad rights over content you generate with Gemini, so cleaning up your own images for your own purposes is well within bounds. The grey area is about context, not the act of removal itself.
Where it gets sensitive is anywhere viewers would reasonably expect to know an image is AI-generated: news and journalism, stock marketplaces that require AI disclosure, design competitions that ban AI entries, or any setting where a hidden origin could mislead. Removing the mark in those contexts can break a platform’s rules even if it breaks no law. The honest rule of thumb: clear it freely for your own workflow, and disclose the image’s AI origin honestly when it leaves your hands.