Dani,
New information: I discovered, looking at some other issues about the new caption keyboard shortcuts, that some of the Beta commands are already in PR 23.3 Release version. Ordinarily, this wouldn't matter if you didn't try to use something that is not supported. I now suspect you were using the shortcut, appropriately, to enter edit mode in the Text Panel.
The command "Edit selected caption text" was an Application level command and a shortcut assigned to it would work in the Timelin
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