Narwhal is a free WordPress plugin I maintain which adds a minimal front end new post box. You may configure it within WordPress' Writing settings. I use the term microblogging loosely because it does not include a character limit like many microblogging services. But, you can very quickly post without a title. The fact that a title is not required and it is quick and convenient on the front side of your blog is why I use the term microblog. If you have some HTML and JavaScript knowledge you can relatively easily add some type of character counter and limit. Also, with a little CSS knowledge you can make it look however you want. The screenshot below is the post form on the Twenty Twenty-One WordPress theme with the default styling. In the settings you can hide certain fields to make it look more like a very basic microblogging post box.
The current version is 2.2.2 and it has been tested up to WordPress 5.6 with PHP 7.3.
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An unsolicited review about the plugin
Screenshot:
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