Yeah, announcing you were going to delete emails unread and expecting the sender to resend when you return would NEVER fly in my office. I’d get executive complaints about that, especially if it went to a client or outside party – if a client can’t reach you, they will reach out to someone else who may not work at your organization and you lose business. I feel like this delete-it-all philosophy would only work for an entirely internal role where timelines are more relaxed, and even then, I feel it’s a bit unprofessional to foist your own catch-up work onto others, especially if they’ve been backfilling for you while you were OOO.
Those of us who are back in the office haven’t bothered plugging most of the phones back in. We aren’t in roles where we get phone calls, those people are still mostly WFH. There is one persistant caller who does not seem to comprehend ‘X is working from home – please email them’, but that’s the only call we ever get.

An out-of-office message is an automatic response to emails you receive that lets the sender know you’re not currently working.
I don’t use the OOO. If you’re supposed to be able to reach me by email, I have already proactively notified you of my absence. If you’re not supposed to be able to reach me by email, your email is already in the junk folder and I think it’s cruel to offer you false hope I’m going to read it upon my return from the rare PTO I take.