If you’re out for the day, I think you literally just need to say “I’m not in the office today, but I’ll respond to your message as soon as I’m back.” If people need an answer to something today, they’re smart enough to figure out they need to ask somebody else.
Huge pet peeve – several of my coworkers still have COVID-related out of office notifications. I didn’t find them necessary in the first place, since everyone was still working from home and should have been checking emails normally, but it’s especially weird now that we’re officially back in the office a couple of days a week. It feels like they’re making a preemptive excuse for responding slowly. I’m surprised management hasn’t said something, honestly.

This is true! The nuclear option also helps the recently returned vacationer understand what is a priority and what isn’t. But, as boyd wrote, “if you just turn off your email with no warning, you're bound to piss off your friends, family, colleagues, and clients.” The blog post offers some helpful steps to make a clean break feasible — they include communicating with colleagues about the sabbatical long in advance, managing expectations of those who rely on you, creating a backdoor for true emergencies, and then, right before going away, reminding everyone about the sabbatical once again.
I hope you’re having an A+ [week, month]. I’m out of the office at this great conference [link to the event]. It takes place on [date] at [time] in [city and location].