My new job provided a template OOO as part of the onboarding brand templates package! I’m sure it might seem like overkill to some, but I’ve had tons of nervous first-job employees ask me what theirs should say, so I loved that they just gave a sample to go from. Also goes a long way in communicating that unique office culture stuff that is usually unspoken/not formalized.
What we need in our work communication is not more professional politeness or less formal, chat-based messaging applications like Slack. We need honesty. The problem is that we’ve conditioned ourselves to see honesty as self-indulgent or disrespectful. I’d argue the opposite is true. Honesty, even if it’s a bit more inconvenient for all parties in the moment, pays dividends later. It builds trust. When my partner Anne Helen Petersen and I were interviewing people for our forthcoming book on remote work, a frequent lament from both middle managers and workers was that they didn’t feel like they knew how to succeed in their jobs; that they were guessing what their superiors and coworkers wanted and, even when they asked, they didn’t quite trust the responses they got back.

Seconded, with one exception: I got one once from a distant coworker which said “I have broken my arm in a kitten-related fall and will be out for (…)”. Everyone else uses boilerplate language so that one definitely stood out, but I thought it was the right level of mildly amusing.
A clear, thoughtful out of office message saves the caller from troubles and inconvenience caused by your unavailability as they know what they should do next. Such a system avoids the negative impact that could come from the inability to respond to calls and messages. Your clients would likely try and contact you again and again, getting frustrated and losing trust in your business.