As the title states, I want to watch MP4 movies on my Samsung S20+ during my cardio walking sessions but would like to be able to resume from the last location if I had to stop and continue later and accidentally closed the app.
MX Player will do this, and I believe it has a setting that makes this default. I know it will ask you if you open a video that you've previously watched a portion of and closed even if it isn't the last thing you watched with the player. It does only work with videos on the device however. This feature might work with videos from the cloud, like Google Drive or Drop Box, but I'm not 100% on that. I don't know of any player that will resume from a streaming source, except for streaming sources that have their own players.
VLC Player might do this as well, just like MX. Not sure if it has a default setting though.