Using Classic Outlook on Windows for personal email, calendar, and contact management
None of your suggestions above work at all.
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This has been an issue for a while. I'm using Outlook as part of Office 365 on my desktop, Dell XPS 8950. While writing an email, all of sudden, text disappears or gets distorted (e.g., some part of the text is shown and the other part is not). After scrolling up and down the mouse wheel, it usually returns to normal.
I've searched for a solution and found almost all suggested solutions say that I need to disable "overtype mode" as below. However, both options were already unchecked but the issue does not go away.
Text disappears as I type (microsoft.com)
TYPED TEXT DISAPPEARING BEFORE MY EYES ALL THE TIME WHILE TYPING EMAIL - Microsoft Community
If you know other causes or solutions, please let me know. This is really annoying and refuses to go away. If standalone Outlook (e.g., Office 2021) does not have this issue, please let me know. Thanks.
Using Classic Outlook on Windows for personal email, calendar, and contact management
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None of your suggestions above work at all.
I have got the same issue last couple of days. It is happening in the Word and Outlook. It is very annoying.
I tried to repair the installation and it didn't help.
I'm having the same issue, exactly, as the original poster. Online repair and adding a new profile didn't change the behavior.
This just started happening yesterday, with a fresh installation of Office 365.
Hi, Joosujin
Good day!
Thank you for posting to Microsoft Community. We are happy to assist you.
According to your description, the issue of your concern that your text disappears or distorted during the typing on your Office 365 Outlook desktop client.
First of all, please be kindly to understand to give an attempt for following steps:
(lower-left corner), and select Apps and Features on the pop-up menu. 
Click-to-run
In the window How would you like to repair your Office Programs, select Online Repair > Repair to make sure everything gets fixed. (The faster Quick Repair option is also available, but it only detects and then replaces corrupted files.)
MSI-based
In Change your installation, select Repair and then click Continue. 4. Follow the instructions on the screen to complete the repair.
In addition, please give it a shot by creating a new profile as below:
If the issue persists, please be kindly to share your detailed client issue and then we can do more searching and test.
Sincerely,
Alex | Microsoft Community Moderator.