Locate where you installed the ray traced mod. In your file explorer address bar copy the path. Seeing as how you installed it you should know where its at but if you dont:

right click on half life in steam and select manage and then browse local files. a folder will pop up. click on the folder "rt bin" and there you will find where the ray traced version is installed.

for me, I have it on an external drive labeled W so mine looks like this:

W:\SteamLibrary\steamapps\common\Half-Life\rt_bin

yours will be different. just make sure you copy yours from the folder address bar.

right click on half life through steam and select "properties"
you will see a box pop up named General. Scroll down to launch options and paste the address you copied from before.

W:\SteamLibrary\steamapps\common\Half-Life\rt_bin\

at the end of it add xash3d.exe

W:\SteamLibrary\steamapps\common\Half-Life\rt_bin\xash3d.exe

now add quotations at the end and beginning along with %command% after the quotes

"W:\SteamLibrary\steamapps\common\Half-Life\rt_bin\xash3d.exe" %command%

and thats it! now if you click play through steam it will launch the ray traced version. Enjoy!