> Buddha said it is super hard or impossible to achieve Nirvana after 1500-2000 years.

Well, that I can agree with. Also according to the Buddha, there are signs that an enlightened being can display to prove their enlightenment. A simple one is that fire does not affect them. To prove his enlightenment, "Ānanda performed a supernatural accomplishment by diving into the earth and appearing on his seat at the council (or, according to some sources, by flying through the air.)"

This is the only modern evidence of anyone meeting the criteria: https://allthatsinteresting.com/wordpress/wp-content/uploads...

You seem to be rather a literalist.

And how should I take those signs of enlightenment then? If not literally then Buddhist scripture is no better than fiction.

Ramana Maharshi got cancer. When the doctor operated to remove the tumor anesthetic was refused. Ramana watched the operation without evident discomfort. He said after that he experienced the sensations of the operation but did not suffer.

Metaphorical, allegorical and symbolic interpretations are some alternatives to the literal one. Sometimes, a story is just a good story.

All religions are fiction.