Want something for sharing anything and everything where even Mastodon isn't decentralized enough?
Make a Web 1.0 website. All you need is a text editor, paint editor, file manager, FTP uploader, and old school website host. You already have the first 3.
Want federation for your Web 1.0 website, too? Adopt button badges for your favorite websites & join some webrings.
Yes, Wordpress-free website hosts & webrings both still exist.
Can't make a website without Wordpress or some other fully hosted browser-heavy application?
Learn HTML and CSS. They're just text markup code and styling code, not program source code; you can make it messy and still produce good pages with less jank than the HTML/CSS code emitted by polished applications.
https://htmlforpeople.com/ is a good enough place to start learning, but many more tutorials and guides exist.
And once you get the courage and confidence to dive in past the wading pool, https://developer.mozilla.org/ is a fantastic reference to keep handy when you get stuck.