I've never been asked for it, and I stopped printing mine years ago, I don't own a printer anymore. Even my work has gone 'paperless' and printing is restricted.

However there is an official US Government website you can use to check your ESTA status - https://esta.cbp.dhs.gov/individualStatusLookup

Hopefully, if I was ever questioned, I could show that on my phone to the agent, as evidence. Or perhaps they could even use it themselves with my details to check. All the details it needs are printed on your passport.