An intermittant bug... (as it happens it doesn't occur as I am reporting this issue).
Open up a STM32CubeIDE project.
Navigate to a project Source Folder, e.g. XYX...Core...Src
Highlight a source file, e.g. "main.c",
right-click "Copy", right-click "Paste". Click "Ok" to the suggested filename "main2.c".
Double-click "main2.c" to edit it, You can't cut or modify any text in the file, nor type in any new text.
Close STM32CubeIDE and launch it again... the file is now editable.
The bug appears perhaps 2% of the time, not a deal breaker but a bit annoying.
