beta 12 is the first Flarum update since the release of the Wordpress extension. I will be testing the extension with beta 12 in the next few days to ensure compatibility. I'll then tag a new release that marks it as compatible.
The extension is using a very restrictive Composer constraint, so you won't be able to update to beta 12 if you have the extension installed until I tag that new version. Thanks for your patience.
As beta 12 isn't a security update, I wouldn't recommend updating right away anyway. It's best to wait until all the main extensions have been properly tested and/or updated.