I just installed Desktop 2020 upgrading from 2017 because email no longer worked with GMail. Now I get "Third Party apps in Google to Less Secure " What to do?

Glad you've upgraded to QuickBooks Desktop 2020, @axel1.

You can set up your email address using Web Mail in QuickBooks Desktop. This way, you will be able to send invoices, reports and more.

Here's how: 

1. Click the Edit button in the upper left corner.
2. Select Preferences.
3. Choose Send Forms.
4. Under My Preferences section, select Web Mail.
5. Enter your email address and choose your provider from the Email Provider drop-down.
6. Click the Use Enhanced Security checkbox and select OK.
7. When prompted, sign in to your Intuit account.

Please check out this article for more detailed steps: Connect your email to QuickBooks Desktop.

QuickBooks will prompt you to enter the webmail password the first time you send an email using webmail.

Also, if the password isn't accepted see QuickBooks will not accept my webmail password for more details.

Let me know if you need further assistance with the steps I've provided above or if you have any QuickBooks concerns. I'm always here to help you out. Take care always.

That is exactly what I do just before getting this error message.  I had the same problem in version 2017 and the tech told me I had to upgrade to 2020 to fix it.