As-salamu alaykum - Do only Muslims enter Jannah?

As-salamu alaykum. The title might sound odd, but I’ve been arguing about this with friends, family and local imams and it’s been weighing on me: is Paradise reserved only for Muslims? A few days ago I had a pretty heated talk with a friend who insisted that simply believing in Prophet Muhammad (PBUH) and in Allah means you will eventually enter Jannah, while those who don’t believe will not. I know being Muslim isn’t that simple, but where I live I grew up with this fear that anyone who doesn’t accept Allah and the Prophet - no matter how good they are - will end up in Hell, whereas believers will be saved. I’m asking because I genuinely don’t fully understand and my knowledge is limited. My friend and many people I asked gave the same answer. I posed a hypothetical: person A is an atheist/non-Muslim who does every good deed imaginable; person B is a “Muslim” who commits every awful crime and sin. My friend said the Muslim will ultimately enter Jannah after punishment, while the good non-Muslim will be condemned forever. I followed up: what if the non-Muslim lived by moral teachings similar to Islam but never said the shahada - would they still be doomed? And what if someone who calls themselves Muslim commits murder or sexual crimes - could they still end up in Paradise? The answers I got made me uncomfortable. I have met non-Muslims who seem more righteous and more in line with Islamic values than some people who call themselves Muslim, and I can’t imagine that those good people would be sent to Hell. I’m asking for a nuanced, compassionate explanation that might ease this heavy question, because honestly this doubt is shaking my faith a bit. JazakAllahu khayran for any thoughtful perspectives.