It's mandatory, but not for all the persons/tenses.
Have a look at this : http://la-conjugaison.nouvelobs.com/du/verbe/connaitre.php
There are several verbs which have the same construction as "connaître" in French. "paraître" is one of them.
You can check out this link :
Google translate only gives you the barest of translations, and even then it is notorious to merely translate word for word rather than what you'd actually say in french. If you look at the previous comments above, you'll see a better explanation of the two and how they are different. Someone also posted a link which goes into greater detail. you can use masculine or feminine with both of those though, the gender has nothing to do with which of those you'd use.
You can find more information here: https://www.cliffsnotes.com/study-guides/french/french-ii/french-ii-special-uses-of-certain-verbs/savoir-and-connaitre