I posted this question back in September, breakaway plugin installation error, and have been struggling off and on to solve the problem ever since. I found the solution today in this post, Installing QIIME on my Mac, specifically the need to follow this link, xcode - Why am I getting an “invalid active developer path” when attempting to use Git after upgrading to macOS Sequoia? - Ask Different, where I learned that I needed to install Command Line Tools from the Apple Developer store (it was free). This solved my problem and I can now download plugins 
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I appreciate the response in the original message. I realize in hindsight that that my question would have been easier to address if I had included that I was using MacOS 10.15 Catalina as it seems to be a Mac specific problem.
Side note, this was also affecting my ability to download some packages in R and it was generally driving me bananas.