Can one forgive people that never apologized or did not even change their behavior?

Listen, this is an important question, and the answer is yes, you can forgive them, but you're not obligated to. In fact, the Torah commands us not to hold grudges against fellow Jews who keep mitzvot. The prohibition against bearing a grudge applies regardless of whether the person apologized or not, because ultimately, whatever happened to you was authorized by HaKadosh Baruch Hu due to your own sins. When you understand this, you realize it's not really their fault - it's your fault for the sins you committed that caused Hashem to allow this to happen to you. Now, there's a difference between forgiving someone in your heart and whether they're forgiven in Shamayim. If someone wronged you and never apologized, you should still forgive them completely to fulfill the mitzvah and to avoid bringing more punishment on yourself. Why? Because if you keep holding that grudge, you're making additional sins, which means Hashem will bring more tests and difficulties into your life. However, the person who wronged you and never apologized or changed? They still have a serious problem with HaKadosh Baruch Hu. Your forgiveness doesn't erase their debt in Shamayim. They will still be held accountable for what they did, especially if it involves sins between man and his fellow. For those sins, teshuva requires them to actually come apologize and make amends. Without that, Yom Kippur itself doesn't help them. So yes, forgive them for your own sake and to fulfill the Torah's command not to bear grudges. But understand that your forgiveness doesn't absolve them of their responsibility to do proper teshuva.