A Lifelong Muslim Facing Doubts for the First Time - Seeking Guidance

Assalamu alaykum dear brothers and sisters, I don't usually reach out like this, but I'm at a point where I don't know where else to turn. I've been Muslim since birth. Growing up, prayer, fasting, and Quran recitation were just part of my family's rhythm. My faith always felt natural-like the air I breathed. But recently, something shook me deeply. Someone very close to me stepped away from Islam, and when we spoke about it, I found myself struggling to explain why I believe. Not because my faith is weak, but because I'd never really had to articulate it before. Now I'm lying awake at night with questions I never imagined asking myself, and it's frightening. I don't want to lose my iman-truly, I don't-but I need answers that stand up to scrutiny, not just well-meaning reminders to 'feel it in your heart.' So I'm asking: What concrete evidence shows that the Prophet Muhammad ﷺ was truly Allah's messenger, and not simply a person claiming prophethood? If someone approached me tomorrow saying they were a prophet, I'd naturally ask for proof. Shouldn't the same standard apply here? I mean this with complete respect-I just need something tangible to strengthen my certainty. This leads to a bigger question: How do we know the God of Islam is the one true God, and not a creation of human imagination like followers of other faiths sometimes claim about each other's beliefs? I should be honest about one thing: I can't rely on 'scientific miracles in the Quran' as my answer. Not because I reject them emotionally, but because interpreting the Quran freely without proper scholarly methodology is itself considered bid'ah. You can't use an incorrect approach to prove a truth. So that path isn't an option for me. If any of you have walked through similar uncertainty, or if you have solid, well-grounded answers-please share them. I'm really trying to hold onto this essential part of who I am. Jazakum Allahu khayran 🤲