Welcome,
When you’re following the instructions in the tutorial here:
https://www.politepix.com/openears/tutorial
Pay extra attention to step 1 from “Preparing to use Plugins”:
Then open up the Build Settings tab of the target app project and find the entry “Other Linker Flags” and add the linker flag “-ObjC”
If you’ve done this already, make sure you’ve done it for the target you’re compiling to.