So I'm gonna be a bit that annoying guy. @m15o created a new kind of journal spec (https://m15o.ichi.city/site/subscribing-to-a-journal-page.html) that seems to get some steam here. It's a clever idea, but it has some mild accessibility issues that you should keep in mind if you decide to use it.
First of all, using an <h2> tag for the date is semantically valid, but it's not a proper use of it. A title is supposed to explain what the content of the next paragraphs is going to be about. Using the date, it conveys nothing special.
Then, the date is used in the year-month-day format for technical reasons (it's how computers understand it), but this format is not shared by everyone in the world and is not human readable. In europe, dates are written in the day-month-year format for example. Instead of "2022-06-01", it would be better to write June 1st 2022.
The issue between readable and computer dates is why the HTML <time> element with its datetime attribute exists in the first place. https://developer.mozilla.org/en-US/docs/Web/HTML/Element/time
So it's not the end of the world, but it's not super friendly either.
My advice would be: use a <time> with a human readable date and a datetime attr inside the <h2>. It's valid HTML according to the W3C validator, you can still use the computer date format for parsers.
Also if you are surprised by the fact that several <article> tags are used in the journal spec don't be, it's actually a good practice! https://www.smashingmagazine.com/2020/01/html5-article-section/
@thomasorus Thank you for the feedback! <time> is definitely something I considered using. Journals are strange in that their entries often don't have a title at all besides a date. Think physical diaries. In those, we just write the date and start writing. That motivated me to treat them as fully fledge titles. Hope this explains a bit the choice. :)
@thomasorus The spec seems to ignore tags (I had an image in my journal a couple of days ago and it cut off the p tag after it) that aren’t recognised. I might test this by adding a <time> and seeing if it cuts off the rest.