Reminder script for GMail: A simple Google Apps Script to create a Google Calendar event (reminder) for any mail (with a specific label). You can then setup ("timed") triggers in Apps Script... (public version of the GMailReminder gist)

GMailReminder.gs

/**
 * Reminder script for GMail: A simple Google Apps Script to create a Google Calendar event (reminder) for any mail (with a  
 * specific label). You can then setup ("timed") triggers in Apps Script (hourly, etc) to monitor your Inbox.
 * How to Use:
 * 1. Log into Google Drive account and create a Google Script.
 * 2. Copy and paste the below snippet into the gs file.
 * 3. Make sure to update the 'reminderLabel', 'calendarName' and 'reminderDuration' as per your preference.
 * 4. Test the script to make sure it is working properly.
 * 5. Setup a time-driven Project Trigger (hourly, etc) to automatically run this script and create calendar events.
 * 
 * Inspired by Gmail Snooze script by Corey Goldfeder
 * http://gmailblog.blogspot.com/2011/07/gmail-snooze-with-apps-script.html
 *
 **/
 
function gMailReminder() {
  var reminderLabel = "GReminder", //Substitute your label here
      calendarName = "Mobile Calendar", ////Substitute your Calendar name here
      reminderDuration = 2, //duration in hours
      label = GmailApp.getUserLabelByName(reminderLabel),
      threads = label.getThreads();
  
  if (threads.length > 0) {
    //get calendar by name
    var cals = CalendarApp.getCalendarsByName(calendarName);
          
    var now = new Date().getTime();
    for (i in threads) {
      cals[0].createEvent(reminderLabel + '- '+threads[0].getFirstMessageSubject(),
        new Date(now+(60000*60*reminderDuration)),
          new Date(now+(60000*60*reminderDuration)), {description: threads[i].getPermalink()});
    }
    //Remove the label from the mails to avoid duplicate event creation on next run 
    label.removeFromThreads(threads);
  }
}

Looks like this doesn't work, I'm getting the following error at line 6:

TypeError: Cannot read property 'getThreads' of null

threads = label.getThreads();

Looks like if you use labels with non-english characters, then the above won't work. See updated solution here:
https://stackoverflow.com/questions/68584353/create-calendar-event-from-gmail