I am also having this same problem on my 2020 QuickBooks Desktop Pro since September 23rd.

I am the only user on this software and I am using Outlook for Office16.

Every time I email a customer an invoice, if I make changes to the body of the email the changes do not remain and only the standard email greeting template is sent. Only changes to the Subject Line of the email are sent.

I now have to email the customers invoice to myself, forward the message, enter the customers email address, make the changes to the body of the standard email template including erasing the sent and forward email time stamps, just so the customer can receive a more professional and personalize emailed invoice.

This is a HUGE inconvenience and very time consuming as our company emails multiple customer invoices including invoice updates per day.

Is there a resolution to this bug glitch yet?  I have been watching this thread all week.