Dragon Gate is a real-time 3D board, so it needs two things this browser has not given it: WebGL 2, and an engine new enough to run the game code. A browser with hardware acceleration switched off is the usual reason, and so are older smart TVs.
Open it on a laptop, a desktop or a phone instead — nothing is installed and nothing needs signing up for.
If you are on a desktop browser, check that hardware acceleration is enabled in its settings; that is the fix in almost every case.