I have this on Stack Overflow (I am posting an answer):
but I haven't posted anything (only flag and votes up) in the last 30 minutes. How can I fix this bug?
This is not a bug but very much by design.
Users with less than 125 reputation on the site must wait between posting answers. We slow down new user contributions in order to ensure the integrity of the site and that users take the time they need to craft a good answer.
And due to recent events the rate limit got increased due to:
the influx of GPT-generated answers that have caused information that is objectively wrong to make its way onto the site.
If you have awesome self composed answers to great questions on your backlog keep them off-site until you're no longer rate limited.
In general all the different rate limits are documented in The Complete Rate-Limiting Guide