"He never cared about it."
Translation:On se o to nikdy nestaral.
so I tried "nikdy se o to nestaral" and it said I should've used ně instead of to?
It is accepted, you probably had some typo in your answer. We do not have any recent report though.
It is similar, but different. It is more about wanting something rather than caring about something.
No, "o" can also be used with accusative. The verb or phrase determines which case to use.
For example, "o něco větší" "larger by something", "o něco zakopnout" "to trip on something", "o něco se vsadit s někým" "to bet something wth someone", "jít o něco", "hrát o něco" "play for something"
The English translations may be somewhat incorrect.