Title Casing... this is a pretty serious issue I waste a lot of time on manually correcting. :P
There are multiple different types of Title Casing too (Chicago, APA, MLA, [...]).
As AlanHK said, most of the automated tools out there cause mistakes. Another problem a lot of these tools do is they only do a SINGLE pass, and they don't take properly take into account punctuation (especially em dashes and colons). They also don't play nice with Roman Numerals or words that need to stay ALL CAPS like "FBI".
And some of the rules get hard (especially when dealing with lowercase conjunctions). Some words can be conjunctions or not depending on usage (which requires a human).
I found this site is pretty decent:
https://capitalizemytitle.com/
But the problem with many of these sites is you have to copy/paste the input one-at-a-time.