Hi there! Thank you for reaching out! Sorry to hear about your issue. I couldn't reproduce this on my Windows machine. Moving this to discussions for now.
Please provide your system info so that we can take a deeper look. In Photoshop > Help > System info > Copy the contents into a text/Word file. You can share it via Google Drive, WeTransfer, or another public file-sharing platform.
In the meantime, here are a few things you can try to fix this:
1) While the Clone Stamp Tool is selected, go to the menu Window > Clone Source to open the panel. In this panel, uncheck "Show Overlay".
2) Go to Edit > Preferences > Performance. Click on Advanced Settings and uncheck the "GPU compositing" option.
3) If the above doesn't work, go to the Performance section mentioned in step (2) and uncheck "Use Graphics Processor". If this works, your GPU drivers might be faulty. Please install the latest GPU drivers.
4) Reset Photoshop's preferences: Please back them up first. Here's how you do it: Backup and restore preferences, and here's how you reset them (please use the Manual method): Reset preferences
Hope this helps!
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Noel