Electron JS: Renderer process does not maintain data type (blob) from Preload.js

Question

Here is a little bit of my preload.js code.

const webmFixDuration = require('webm-fix-duration').webmFixDuration;
let fixedBlob = "";
contextBridge.exposeInMainWorld("api", {
     fixDuration: function (buggyBlob, duration) { 
         if(buggyBlob instanceof Blob) {
             webmFixDuration(buggyBlob, duration, "video/mp4").then(function(value) {
                 fixedBlob = value;
             });
         } 
     },
     getFixedBlob: function () {
         return fixedBlob;
     } 
});

Then, here is a little bit of my renderer code.

 //recorder is a mediaRecorder
 recorder.onstop = function () {
        let mostRecentChunk = [];
        mostRecentChunk.push(...chunks);
        blob = new Blob(mostRecentChunk, { 'type': 'video/mp4' });
        let milliseconds = seconds * 1000;
        window.api.fixDuration(blob, milliseconds);
        let realBlob = window.api.getFixedBlob();
        videoURL = window.URL.createObjectURL(realBlob); //This line causes an error
        //Before you ask, yes videoURL is declared previously in the code
        //Rest of my code goes here, but it's irrelevant
  }

Now, the webmFixDuration function returns a Promise. As such, the getFixedBlob() function should return a blob. Therefore, the line in my renderer process videoURL = window.URL.createObjectURL(realBlob); should work since the createObjectURL function takes in a blob. However, the console in my application reveals that this line creates an error that says that the parameter realBlob is not a blob object. If I replaced the offending line in question with:

if(realBlob instanceof Blob) {
  videoURL = window.URL.createObjectURL(realBlob);
} else {
  console.log(realBlob);
}

The application goes to the else condition, and the console reveals realBlob to simply be an Object (not a blob), and the object doesn't even give any details in its properties.

In short, it seems that even though my preload.js function getFixedBlob() returns a blob, my renderer process is for some reason reading it as only being an object.

How can I get my preload.js to return a blob?