2. Yes, doubting lived experience of Black, Indigenous, Asian, Arab, etc. people is itself racist.
Just don't.
And yes, asking for proof is doubting that lived experience. If you think you are the first white person descending on a thread to "just ask questions" – you are wrong.
Instead, go read the threads I link in the next toot, and follow their authors. Then go read through their other threads. There is plenty of receipts and proof, and most importantly context and explanations, in there.