They’re probably inserting the ads “on the fly”. It can be finicky depending on codec, but doable.

Not many are officially supported, but there are a few. Baldur’s Gate 3 is one surprising example. Many Paradox games are also supported, like Cities Skylines. Stardew Valley, Terraria and Hades as well.

I’m pleasantly surprised Linux is way ahead of OSX. This looks really good!