If you set up the static site generator as a CI/CD action in you favorite git provider, can work with both hosted GitHub, GitLab, etc. or self hosted Forgejo [1], you have both version control for your blog as well as an automatic way of publishing.

Sure, the UX is not that great as with a dedicated interface like substack, but building a Hugo site is really just editing markdown files anyway, most mobile git enabled editors should be able to do that.

[1]: https://home.futuretim.io/posts/hugo_build_and_post/

You could use Substack/Blogspot/Mastodon themselves as your "static site generator".

POSSE (the concept linked here) is overrepresented in relation to revealed preference. PESOS (publish elsewhere, syndicate on site) is more compatible with how most people (including nerds) actually use the Internet; for all the talk about static site generators and "owning" your own "digital garden" >9/10 people would fall somewhere on the embarrassing part of the curve from the "Blogging vs. Blog Setups" comic. <https://rakhim.org/honestly-undefined/19/>

If you migrated to a fediverse instance with longer post length limits, you could use that to actually blog/post while mobile, and meanwhile you have a script on your homepage that "lazily" syncs those posts to your static site—

When anyone visits your homepage, they see your site as it was when you last built it.

When you visit your own homepage, it automatically fetches your social media feed, patches the previous input to the SSG with the new content, and then uses the APIs of whatever you're using to host your site for rolling out the new posts.

You can write your posts in Markdown, use Obsidian to sync them across devices, and render the pages in Quarto. This might not let you publish from mobile, but you can at least write them anywhere you want.