Web video player with fluent design was removed?

From the very first build, you could set to enable flag "Web Platform Fluent Controls".  IDK what exactly it should do but it also replaces standard chromium player. The fluent player looked similar to Windows 10 Movies & TV with square buttons and additional functions like skip forward\backward. A few months ago for some reason icons on the buttons became transparent and were visible on hover only but it still worked. The build 79.0.309.5 reverts chromium player even when the flag is enabled, build 80.0.318.0 removes the flag completely(?)