Embedding someone else's browser game on your own page looks like one line of HTML. Then you ship it, and a user says the controls don't work.
A key press only reaches the embedded game if the game frame has keyboard focus. On a fresh page, focus sits on the wrapper. The user clicks Play, the game starts rendering, and then nothing responds — because the click landed on your button, not inside the frame.
The fix is guidance, not code: tell the user to click inside the game area once, and keep that line next to the embed instead of burying it in a FAQ.
x-frame-options: SAMEORIGIN, a platform-side outage, and an aggressive privacy extension all produce the same blank rectangle. Your page has no idea which one happened, so it should not claim to know.
What I ended up doing: a 60-second timer starts when the iframe is created. If no load event fires, the page shows a plain notice that the embed didn't load, plus a direct link to the original game page. That link is the difference between "this site is broken" and "I can still play".
If the site ships five languages, the failure notice needs five versions that mean the same thing. A translation that turns "embed failed to load" into "game doesn't work" is a support ticket waiting to happen. An embedded game is still someone else's game. The wrapper gets a visible credit line, the page states that it is unaffiliated, and no form or comment claims ownership. That matters more than any meta tag.
That is the setup at noomicheems.online, an independent, unofficial companion site for NoomiClone by jamesnorth. The focus and fallback advice lives on the guide and the troubleshooting page.