I might sound nitpicky but the language is important. “Might” or “may be” or “slower than usual” are vague and don’t offer the sender all that much information about when you’re really going to respond to them. Worse, they do a horrible job of protecting the time of the email receiver who, as the responder notes, is not in the office! Such a responder implies that, not only will the vacationer reply to the email, but they may not even miss a beat. They may be slow to respond, but they also might not.
When the holidays roll around, many companies decide to hold holiday parties to celebrate with employees. However, announcing such a party requires releasing pertinent information, such as when, where, and additional details, such as dress code and expected activities. Doing so helps employees understand the event and manage their expectations.

Yeah, it’s very strange. I understood changing voicemails to explain that the line can’t actually be answered, but someone is checking the messages and will respond (though that was also only an issue for the first few months), but they had no reason to even mention it for email. I started my job 3 months into lockdown, and by that point, procedures were in place to pretty much allow us to operate normally, albeit with a lot more done electronically than before.
At my old job, you used to nominate a contact for when you were out of the office and there wasn’t an obvious person to contact. One department was so small that they all just put the all team email so they never had to change it. Trouble is, it turns out Outlook team emails by default only accept internal messages :X