Most modern browsers (Chrome, Edge, Firefox) can play MP4, WebM, and many streaming formats directly. Just drag and drop a video file into the browser window.
Modern "all-in-one" players are designed to handle complex media files that standard system players often cannot: Broad Format Support vivdisk player online
Run a security scan (Windows Defender, Malwarebytes). Avoid entering personal info or downloading anything from that site. Most modern browsers (Chrome, Edge, Firefox) can play