Do you know if a screenshot is enough, once you have this response?
No idea whatsoever. We were not asked about it. Had we been asked we could have produced it in an instant.
We know enough to keep our ipads or phones charged up enough when proof of vaccination, etc. was requested by carriers and by various customs/immigration folks. Same story pre covid where once in a blue moon an immigration agent would ask us for proof that we had an exit flight booked or a local address.
This business about keeping a charged unit to access important electronically stored information required for travel is fairly basic to most travelers and has been for quite some time. Covid or no covid, ArriveCan or no ArriveCan. Not to mention hotel reservation confirmations, airline locator codes, etc.
If you rely on electronically stored travel data instead of hard copy docs then one should have the very basic smarts to keep the unit charged to a point where retrieval is a non issue. If not, don't blame others. Look in the mirror for the real culprit.