I sincerely thank everyone again for their extremely kind and helpful comments. They are all very much appreciated. I did go through the suggested process, which more permanently makes Libre open its associated files rather than needing to do that for each file individually. But beyond that unfortunately nothing changed, with the same odd and altered formatting observed from what I recalled of my most recent work and the same new notice popping up upon opening my LibreWriter documents.
However, and while very embarrassing to admit, I then did some further investigation largely in view of the kind comments regarding the new installation possibly changing my installation of fonts. While it did not seem like that long, and in needing to critically attend to other parts of the business most recently, I guess it has been about a couple of months now since I actually did any editing work on the book. And I have had it on write protection and not taken it off for quite a while now and not saved any newer versions since.
And in my first Libre file opening since upgrading to MS Office 2024, I first very broadly noticed discrepancies and alterations surrounding figures, with many of their captions missing or placed differently, and altered spacings between images and surrounding texts as examples. And in looking a little deeper, I also found various captions that are of different font sizes (I used the same font style throughout the work) and also italicized in certain places but not in others. And I find it highly unlikely that these types of discrepancies would be caused by any formatting differences between my current LibreOffice version and my very recent upgrading of MS Office from 2003 to 2024.
So I looked back into my editing notes in more detail, and it now appears very likely that I actually produced and left these elements exactly as I have found them upon my most recent openings of the files. And while I will need to thoroughly inspect and confirm this yet again, it is looking more like no notable formatting alterations really occurred due to the update installation of MS Office. While I was primarily attending to the far more crucial textual content, I really thought I had completed more work on the formatting of the figures than I apparently have to this point. So, it looks like I owe everyone a double apology and hope I have not wasted too much of everyone’s time.
Assuming and hoping that this continues to hold true I just need to make two, more minor decisions before I soon get back to work on the book. One is the new prompt I am getting, upon initially opening really any Libre file, about whether or not to change the LibreOffice default file format registrations to be or include .odp and .ods file formats and to have Libre open them by default. And the other is whether or not to update Libre before continuing from my current 7.6.7.2 version (not that old yet) to the newer 24.8.3 version that I keep being prompted to do, hoping that I do not get any notable formatting changes or other surprises there.
So naturally I would be grateful for any further comments regarding either of these. But if not, I understand and should hopefully be able to navigate through these elements, which seem a bit less severe than what I thought was going on earlier. I once again sincerely thank everyone for their gracious input, and I am sorry for any inconveniences caused because of the formatting issue(s) that I really thought was taking place earlier.