The plugin release is scheduled for February 9, but, due to the number of changes this version contains, it is a good idea to do a short Beta test and see if anyone else reports some issues with the plugin, and maybe add some more fixes into a stable release.
As previously announced, the new version will include a large number of core changes, and you can read more about that in that announcement. Right now, it is important to know, that all the features planned for version 6.0 are done in this Beta version, and there will be no more new things added before the stable version is released next week.
Make sure to test this Beta version on the staging or development websites only! Do not use this Beta version on live websites, because there might be potential bugs present that can crash your website. Also, plugin system requirements have changed, so make sure you are using WordPress 5.3 or newer, and PHP 7.2 or newer.
The focus for this Beta is to see if things don’t get broken after the update, or some settings are lost. Due to the core changes in how some plugin features work, test bbPress integration (no longer extension, and now activated automatically), visual aspects of the metabox editing, loading of plugin CSS and JS files. Also, test the behavior of new HTML5 related settings for meta fields – to use native browser color and date/time pickers.