Miffy is playing Super Mario 64 https://www.twitch.tv/miffynwn
However there is some more to this. It seems Miffy is the reincarnation of another vtuber, Iris Fuwa (which she announced) that had vanished last year.
https://x.com/Miffynwn/status/1965570358830055589
She switched back to the old model but says she hopes to update it into being a bear like the one she had been using and will be keeping her content the same so presumably that means she'll be retro gaming still. Personally I think the bear she had been using was better than this one if this one is going through an update anyway but not too strong of a feeling.