I like the idea of a shorter character limit as it nudges users to a specific mode of interaction: short thoughts/updates and not long-winded soliloquies. It's signalling that interaction with this platform doesn't demand much of your time or attention. I don't know what the about page has to do with it, but you have to draw the line somewhere.
That said, I'm not a social media user besides HN I guess.
For perspective: you just commented 404 chars. Your first paragraph alone was 346.
My comment on the about page was that it needed more than 280 chars to communicate what the app is about - even the title + intro exceeds the limit.
If it is truly believed that 280 chars is enough to communicate an idea, then the about page should follow that philosophy.
I'm considering raising to 500. Care enough to open an issue[0] so that maybe there is a discussion we can track?
[0]: https://github.com/stagas/textlog/issues
Honestly, I don't really care that much. The project looks like fun, and I wish you the best with it, but I don't really post on microblogging platforms myself.
I just wanted to give a bit of feedback as someone who reads them - and point out that on almost every twitter/bluesky submission to HN they are using ways to work around the 280/300 char limitations.
To play devils advocate - 500 also seems a bit arbitrary ;) If I were making a platform like this myself, I would go for a power of 2 that makes sense for storage/buffering. Maybe 1KiB including all meta, etc. You could comfortably fit a post the size of your about page, and all associated meta in that - even when serialised as JSON or something. I'd go from there and work backwards to come up with a size that has a real technical purpose.
Make it a setting and let people decide for themselves.