You may need to update Windows 11.
Seems that this new API isn't perfect just yet.
In the meantime, use Glasstron for now.
npm install glasstron-clarity
Then define Glasstron in your main process:
const glasstron = require('glasstron-clarity');
Then for your window, just enable blur, so add this option to it:
blur: true
This will give you Acrylic, since Mica support never made it into Glasstron.
More on Glasstron Clarity: https://sudovanilla.com/code/Korbs/Glasstron-Clarity/src/commit/7f5258b8acaaf742f13a10a18aa02369abe0e684
More on Electron's API for built-in support for Acrylic/Mica: https://github.com/electron/electron/pull/38163