I've coded up a little private journalling app that's like a one-person social network. I've called it "YouSky”. It's free.
https://yousky.veryuseful.app/
It has replies and hashtags. Works kinda like you expect. Pretty basic. But does a job.
This is 100% private. No servers. No tracking. No cookies. All data stored in your browser.
You can export to a JSON file if you want to backup or move your data.