Brake fluid only going to one caliper

If you are only getting fluid to one corner, then the best thing to do is go back to the starting point and trace it through the system and find where we have it and then where we lose it.

Clearly the likely issue is the master cylinder so let's start with bench bleeding the master and find out how much is coming out.

I attached the process below on how to do this.

Also, when you say you did away with the proportioning valve, you mean you just routed the lines directly to the calipers and not through the valve? Is there a reason you did this? Were you bypassing it to test to see if that was the issue?

If we find that the master is the issue, here is a guide that will help with replacing it:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Please see the info below and let us know what you find with this. Thanks