Here’s the video referenced in the article.

It’s honestly more about being able to run path tracing with a low performance hit than it’s about the steam deck specifically being able to run it.

The key part of the article is:

The video shows the settings menus before gameplay begins and reveals that the game is running at 864 x 486 resolution, with secondary bounces disabled in the RTX Remix developer menu, which seems to be the secret to maintaining a decent frame rate on the Steam Deck APU.

Portal RTX uses 4 raw bounces on ultra settings, which is enough to bring any modern GPU to its knees at high resolution, so disabling secondary bounces entirely and lowering the res really takes the strain off that poor Deck.