I'm a fan of WriteFreely [0] as a no-frills blogging platform. So far it's had negligible resource use, and I like that it looks like a stripped down Medium or Substack without the social features. It takes Markdown formatting so it's not fully WYSIWYG, but it autosaves so it's easy to jump back and forth between the draft and its preview. Oh and there's decent support for MathJax though you need to enable it in the admin console beforehand.
As for discoverability, it supports ActivityPub federation, so people using Mastodon or [insert trendy federated app] can get updates when you publish a new post.
About the only downside is that it doesn't come with automatic image upload/embedding, so you'll need to manually upload to imgur or imgz and embed using the usual markdown syntax. Or comments, although that appears to be a deliberate design decision that I honestly agree with.
Netlify CMS is nice in that it has a hosted WYSISYG editor for Markdown files. It's nice in that it fulfills your requirement of not using HTML and CSS every time, but since it is using Git and Markdown, it is still portable. [1]
They are provide nice templates to get started. [2]
[1] https://www.netlifycms.org/ [2] https://www.netlifycms.org/docs/start-with-a-template/
Maybe try Medium or Substack, or for control over your server, Mastodon/Pleroma.
2 things: 1. how you host it is largely irrelevant to engagement, unless you buy into the sales pitch of Medium. 2. use forestry.io and you can have a nice wsyiwyg editor for your static blog. They've got a opensource sucessor now that's even more... WordPress like, for lack of a better word. Those content section block things whose name i forget.
Also, why are you mucking with css/ html to embed a photo in a static blog? Most static blogs moved past that over a decade ago.