How do I add a distort effect to my stereo in?

It won’t let me select it as an source in the effect channel settings

Could you be more precise, especially about the items put in bold ? I guess that you’re for a whole rewriting of your OP, because at its present state, it’s meaningless…

Sure

I am trying to run my electric guitar trough my Steinberg UR12, into my pc and into Cubase 13 to play it, where the input shows up as ‘‘Stereo in’’

Whenever I try adding effects like amp sim or distort it wont let me select it as a source in the channel settings of the effect

Now, this makes sense… :wink: Welcome, by the way !

But an amp sim of any kind should be used as an insert in the audio track dedicated to the guitar recording. What do you have in your Inserts list ?

Beside this, using a Stereo input for a mono source such as a guitar isn’t the best thing to do. It would be better to set all your inputs as mono input busses in the Studio > Audio Connections > Inputs panel :

This doesn’t prevent you to use a stereo track for added stereo effects use : i do this all the time. Beside this, as you are using the AI/LE version, you won’t be able, I think, to set the amp sim in the signal path before the recording (no input tracks available). This doesn’t prevent you to use it and, eventually, render the track with the amp sim applied, after this, of course.