Jenkins - load global pipeline library from file system instead of SCM?

It seems that this is currently not possible. But you can easily create a local git repository and use it like an SCM without any remote hosts.
To run the git repo, use the following commands in the root directory of your shared library (for example, C: \ Users \ Jenkins \ protocol-shared-library-test):

git init
git add .
git commit -m "init"

      

        
        
        
      

    

Then in Manage Jenkins->Configure System->Global Pipeline Libraries

you can point the Project Repository

local repo using the file URI file:///c:/Users/Jenkins/pipeline-shared-library-test


This approach works great for me.