Is it normal to read backwards?
Mostly.Normal for most people
Yes—reading words or sentences backwards for fun or as a mental challenge is a harmless quirk. If you mean you can’t read normally or words seem to reverse involuntarily, that’s a different thing.
If you mean choosing to read text from the end to the beginning, sure. Some people do it for amusement, to test themselves, or just because their brain finds it oddly satisfying. It’s not something everyone does, but it’s harmless.
If you mean words regularly look reversed or reading forward has suddenly become difficult, that’s not the same habit; consider getting that checked out.