miserable assembly reference

Unity is having trouble finding my DLL. I have a DLL that I’m able to successfully load in visual studio by adding a reference, but I’m still getting errors in Unity.

The DLL is in .NETframework 4.6.1, and I’ve tried upgrading the unity .NETframework to 4.x, installing the relevant SDK in the visual studio installer, using different versions of unity (2022, 2020, 2019), all no good.

I know the DLL works because I’ve been able to compile it outside of unity, but my goal for this project is to have it running in unity without hacky IPC.

Here are a few references to other things I’ve tried that don’t work:
A reference to the dll could not be added
.dll file not accessible
https://answers.unity.com/questions/458300/how-to-use-a-external-dll.html

please save me stack overflow.