As I understand it there is no intention to add support for plug-ins within the Windy mobile App. (Although I would be happy to be wrong about this).

However, as described in the installation instructions within the SoarCalc ReadMe.md file that you can find here...

https://github.com/tomgooch/windy-plugin-soarcalc

it is possible to use plug-ins within a browser on a mobile phone which will achieve pretty much the same result.

BUT, since I wrote the ReadMe file things have moved a little in the wrong direction. You can still install the plug-in by navigating to https://www.windy.com/plugins however you can no longer open Windy.com with the plug-in active by navigating to https://www.windy.com/plugin/soarcalc (or any other plug-in so far as I am aware). Instead, it is necessary to go to https://www.windy.com/plugins each time, select SoarCalc and then "Open plugin" from there.

This works but for some reason it is no longer possible to tap on the items shown in the plug-in to see the tooltip / description of the parameter. The parameters are however, fully described in the ReadMe.md file.

I hope you find this helpful.

I would be very interested if anyone can tell me why urls like https://www.windy.com/plugin/soarcalc no longer work. If this is a permanent state of affairs I will update the ReadMe to reflect this.