You’re right - it’s great to be able to crosspost, but every fediverse software is totally allowed their own features and if other systems don’t display it correctly, that’s also ok.

But in this case, Mastodon really is missing some kind of “group” feature. We kind of have this with the a.gup.pe - Tool, but it would be nice to bring some order into that chaos.

You should at least play around with the export options and do regular exports. You really don’t want your diary of over 5 years to be stuck in an unmaintained app. And since this seems to be supporting exporting into markdown - maybe try an export and checkout logseq or Obsidian?