The 4 canon gospels do not actually have any hard evidence indicating who actually wrote them.
They initially circulated for decades, without titles, without recorded authors, anonymous attribution... untill eventually names were just assigned to them around 200 AD/CE, roughly 130 to 90 years after they were first written.
Bart Ehrman isn't just some random guy with a blog, he's one of the most academically influential and well known Biblical scholars, got a PhD around 1985, been publishing papers and books on this sort of stuff longer than I've been alive.