The plugin imports only OLD version of YAML format. When Microsoft remove MSAPP and JSON formats, the plugin will reflect on it, and new YAML format will be supported (without fx.yaml)
DesignKit 2.5 version can import particular YAML file located in your local storage.
How to import YAML file?
How to download and unzip MSAPP file you can find here:
When you did steps in previous sentence and your YAML files are located in your local storage, you can click on ADD YAML(s) button, and select your files.
Your selected files will be imported to the Figma file.