How do I stop autocorrect from changing the first letter of these abbreviations to uppercase at the beginning of a sentence?
Filed tdf#121779
Try Tools | AutoCorrect | Options and uncheck whichever options associated with Capitalise first letter of every sentence you want to disable.
If this answer helped you, please accept it by clicking the check mark 
to the left and, karma permitting, upvote it. If this resolves your problem, close the question, that will help other people with the same question.
I see that I can uncheck “Capitalize first letter of every sentence” but that’s not what I want. I do want AutoCorrect to capitalize the first letter of every sentence, except in special cases like mRNA or fMRI.
It looks to me like LibreOffice can’t handle that.
(Some think such abbreviations don’t belong in the beginning of sentences anyway. I disagree though.)
Implemented for 6.3. There, the utility of list for words with two initial caps is extended to also include words with small initial characters.
Cool, thanks!
I just installed the current version in the hope that you meant 6.1.3 rather than 6.3, but you did mean 6.3… I’ll wait.
Yes, you are right 
- I really meant 6.3 due to be released in next august (I have just pushed the change; you may see that in the bug I filed for you and mentioned in the comment to your question).
Nice. Thanks for all that work you do!
There’s a suggestion for a workaround on the bug page:
“tommy27 2018-12-05 09:48:31 UTC: makes sense. valid enhancement request. in the meantime a workaround is to put some specific autocorrect items such as “IPhone → iPhone” and “FMRI → fMRI” etc. etc.” I just tried that, and it does not work for me. “Capitalize first letter of every sentence” wins.
and it does not work for me. “Capitalize first letter of every sentence” wins
Confirm.