I am at an opera house in the countryside (i.e. without reception) and shall return to the office on XX.
An out of office email is an automatic response you can set up to be sent when someone tries to get in touch with you whilst you’re away from the office.

I’m the same. I don’t find it condescending, it’s kinda eye-rolly but also kinda charming! I get why it could be annoying if you need info quickly. But really, why not inject a little silliness into boilerplate messages like this, as long as it’s not disrespectful or really out of step with your field culture?
There’s a grim, apologetic vibe to these messages — I’m sorry I’m taking time for myself but I’ll try to check in on occasion! They’re a vivid reflection of a work culture that valorizes constant productivity and the near-total overlap of work and life. But they’re also do a terrible job of what they’re intended to do, e.g., set realistic expectations for both sender and recipient. A vague OOO message traps both parties in an uncomfortable liminal space where both productivity and rest go to die. The original sender is left unsure if they’ll be getting a timely response or a whether the email will go ignored for a time or forever. The original recipient has taken what is a rock solid excuse (time off) and cheapened it, offering a backdoor for email guilt to creep in.