Thanks for the report, @user1675!
This is a known issue: Markdown preview flicker on mouse movement inside table - #4 by deanrie
I’ve linked your report to our existing bug report, which helps us prioritize it.
As a workaround, you can use VS Code’s built-in Markdown: Open Preview command (Ctrl/Cmd+Shift+V), which opens an HTML preview of the markdown without the flicker.