MOV Compressor re-encodes .mov files, such as those from iPhones, Macs and cameras, into H.264 MP4s. It has High, Medium and Low presets, a target size in MB (approximate) and 1080p, 720p or 480p output. The site says processing happens in a browser worker and that media is never sent to a server.
It is free to use, and the site says there is no signup, no watermark and no daily limit. It needs WebCodecs, so use a current version of Chrome, Edge or Safari on Windows, Mac, Android or iPhone.
I kept getting huge iPhone MOV files that were too big to share or upload, and most online compressors required uploads or signups. So I built one that runs entirely in the browser.