I understand the %20 representing the Space character for URLs, but I believe you're calling Node FS and its adding these signs in when Node FS should use literal spaces, the failure is occurring here: node:fs:561
You can recreate this issue quite easily I believe;
1. Create a new RPG Maker MZ project, then in your file system explorer, navigate to <Game Folder>/js/plugins and add a folder with a literal space (e.g. "Plugin Test"). Add a known working plugin into this folder.
2. Within RPG Maker MZ, go to your Plugin Manager and remove all plugins, then add the plugin that is contained within the "Plugin Test" folder.
3. Save and playtest the game, after one playtest, use RM Cook Tool Deluxe and attempt at building a Test Build, after the build is finished, try executing the game.
The expect result should be that the game will launch but you'll be presented with an infinite load screen, opening the developer console presents the issue and cause.
If you'd like, I am more than happy to record an example of this in action incase you cannot reproduce the issue yourself.