Many different players exist for video, but here are a few recommended ones:
MPV is a open source lightweight media player. It is intended as a command-line application, making it's user interface extremely minimal, however, many frontends exist for mpv, giving a more complete GUI, such as Celluloid and IINA. It has wide codec and container support.
TODO: MPV keyboard shorcuts
VLC is an open source media player and toolkit. It supports almost all video and audio codecs in common use.
Download instructions for VLC on all relevant platforms can be found at VideoLAN's website
Media Player Classic - Home Cinema (MPC-HC) is an open source media player designed exclusively for Windows 7, 8, 8.1, 10, 11 operating systems. Recognized for its simplicity and efficiency, MPC-HC provides users with a streamlined and user-friendly platform for playing a diverse range of audio and video file formats. Its lightweight design ensures smooth playback without taxing system resources. While the official development ceased in 2017, the community-driven MPC-HC on GitHub continues to provide updates and support.
The latest un/stable builds of MPC-HC, maintained by the community, can be found on clsid2's MPC-HC repository.