A little background to the issue High Bandwidth via Direct Play on Windows 10
And it does not only affect streaming connections, but also the rather low-bandwidth connection to the phone’s internal storage. Using an SD card for media storage will make it significantly worse.
As for ‘optimize for streaming’ (sometimes also called “fast start”): https://blog.dareboost.com/en/2018/01/optimize-your-mp4-video-for-better-performance/
(start reading from " Start playback before downloading the entire content")
