Yes, that regex pattern is definitely "the bomb" for finding the sort of issue you wish to find. It took me a while to parse it apart to understand it in its entirety; I'm a bit rusty these days. Now that Windows 10 has PowerShell, you could even use it in conjunction with the grep (short for get regular expression and print) command to have specific lines where the issue is found produced so that you can easily search for those lines. The thing I don't know is whether you can actually run grep against a .docx document or if you'd need to save a plain text or rich text format version of the file for processing.
In any case, even if there is an intermediate step, you can use this method to quickly identify the vast majority of instances of uncapitalized sentence starts, capital letters embedded inside words, or capital letters on words within sentences where they'd typically not be.
Brian - Windows 10 Pro, 64-Bit, Version 1903, Build 18362
The color of truth is grey.
~ André Gide