Valve sure do give a lot of love to their games (okay, most, I hear the rumbling of TF2 fans in the background) and a new update has rolled out for the original Portal to help the Steam Deck.
Portal is one of the titles that Valve updated with DXVK-Native, which allows the classic to run using Vulkan instead of OpenGL, an update for this title I somehow missed from back in late February. They did the same for Portal 2, Left 4 Dead 2 and the Half-Life 2 series. The problem with DXVK for both Native Linux titles and Windows games in Proton, is that it can stutter while it builds up a shader cache.
The new update for Portal lists that it "Added DXVK cache priming for the Steam Deck", which should reduce any stuttering to a minimum for Steam Deck. You can use DXVK to get Vulkan on a Linux desktop too if you run "-vulkan" as a launch option.