If I say "mostly" at the very end of the sentence, would it change the meaning of the context?

I saw people crossing their fingers after lying. Does that gesture have the same meaning as "fingers crossed?"

This is a very good question! "Fingers crossed" is taken from the hand gesture of crossing one's first and middle finger to indicate that one hopes things go well. It's a bit of a superstitious gesture/expression that means "may all go well". On the other hand, when a person crosses their fingers behind their back when they lie, they are asking for protection from the consequences of lying - basically asking to be safe or unharmed from whatever happens if they lie or get caught lying. So they do have somewhat similar meanings! Ex: I saw you cross your fingers behind your back. Did you lie? Ex: Fingers crossed that it won't rain tomorrow, or our vacation will be ruined.

What does "backed by" mean?

To be "backed by" in this context means to be supported or defended by something or someone else. It is also common to use the phrase "backed up by" to express the same meaning. Ex: Many of his friends backed up his decision to quit the soccer team. Ex: The town backed up the owner's choice to expand the restaurant.

What is the meaning of "cover star"?

The speaker has used "cover star" as a way to shorten the phrase "star (celebrity) on the cover of Billboard magazine." It is common to shorten phrases in this way for news reports or interviews, in order to make the language shorter and more concise. Ex: Ariana Grande is the current cover star of Forbes magazine. Ex: Billboard Magazine cover star, John Legend, has released a new song.

In what situation can I use "suit yourself"?

You can use "suit yourself" when someone has decided to do something against your advice, offer, or suggestion, because they want to do something the way they want to do it! But it's not a serious tone. It's more casual with a slight tone of indifference. Kind of like saying they have to accept the outcome of their decision, or as if saying, "if that's what you want, go ahead." Ex: You don't want to come to the movies? Alright, suit yourself. => if that's what you want Ex: Person A: You want a ride to school? Person B: No, I'll walk. Person A: Suit yourself. Bye! => indifferent tone

I've heard that there are many bears inhabited in North America. Do people in North America also devour the bear?

Bear meat has been consumed in North America for hundreds of years by both Native peoples and colonialists, but it is not a commercially-popular meat, nor do people often consume it in restaurants or at home. It's more popular today with hunters, as bears are wild animals and difficult to hunt.