Translation:Sorry! No worries!
"No problem" is far more common in North America, though "no worries", which is popular in Australia, is gaining ground.
The English usage doesn't exactly track the Chinese usage.
I'd say "no problem" in response to someone saying "thank you", not "sorry". I'd say "no worries" if someone said "sorry".
I understand it's not about national pride, but about not forcing just one variant arbitrarily on everyone. I'm a Spanish speaker, and I trip over this one every single time. And there's no Mandarin from Spanish course, in case you're wondering what I'm doing here. I bet there are lots of non native English speakers.
This phrase in Chinese has a lot of acceptable English translations (from the more formal to the casual) and needs to be corrected to include them. Duolingo for Chinese study seems to be challenged as to its translations being too narrow / literal. In this instance all of the following should be acceptable:
Sorry! No worries!
Excuse me! No problem/worries! Pardon me! That's OK! I'm sorry! No problem/worries! I'm sorry! That's OK! etc.
对不起 means sorry (what you say as an apology). 没关系 is dismissing someone's worry about a matter: it's not important/it doesn't matter/that's ok/don't worry about it/etc. You can say 没关系 after someone appologizes to you. Note: 关系 does not mean "problem." 关系 means something like "how much something matters". When you have a good relationship with someone, like having good connections, that is having good 关系 with that person.
One distinction seems to be that "对不起" is used only for owning up to a mistake of the speaker's, whereas "抱歉" can be used for expressing regret about a situation that the speaker didn't cause (though it's not limited to such situations). Another is that "抱歉" is a bit more formal, in a sense, and less emotional, and therefore it carries less weight, sort of like "apologies".
I welcome corrections as usual.
I'm not a native Chinese speaker, if that's what you mean.
You can read about positive and negative potential complements using "-得起" and "-不起" here:
(The sense is often about being able to afford something or not, but as with other similar potential complements, fundamentally it's about whether or not the action in question can be achieved.)