There are several mods out there to let you play Half-Life: Alyx minus a VR headset. One that's currently still in the works is being developed by SoMNst, who was unfortunately slowed down by catching Covid earlier this year. SoMNst has since recovered and development is moving along, with the latest update showcased in a 37-minute video.
Among the new features: working pens. You can draw with them using your mouse, as demonstrated at the start of the video when SoMNst doodles an impressive Gordon Freeman on a window, before adding devil horns to Eli Vance on a monitor. This latest update also features better collision, UI improvements and custom hints, custom items (a pipe), changes to some of the more complex puzzles to insure they work for flat screen players, and the in-game menu now works properly.
Watching it in action, moments like the scene where you're captured and the Combine demand you raise your hands do lose something in the translation, as do tactile motions like climbing ladders and flicking objects with your wrist, but it's still worth it to make Half-Life: Alyx playable for people who don't have VR. Hell, I've got an Oculus Quest 2 and I still haven't finished Alyx because I play VR games in such short sessions. If it was flat-screen I'd absolutely have played the whole thing by now.
SoMNst's mod isn't available for download yet, but you can keep up with progress on YouTube (opens in new tab) and Patreon (opens in new tab). If you want to play Half-Life: Alyx without VR right now, alternatives are available.