Hello,
Unfortunately there is no justify button in that additional tab editor for formatting of text.
But you can try the below article for this purpose:
https://www.wpbeginner.com/plugins/how-to-add-underline-and-justify-text-buttons-in-wordpress/
I have implemented the plugin mentioned in the above article and it works just fine at my test site. You can check the result in this screenshot: https://jmp.sh/grs2HGE
About the bold text and the spacing, these things working just fine at my end. To fix this try with only theme required plugins because might be some third party plugin is the cause of this issue.
Screenshot: https://jmp.sh/d50VtAY
Best Regards.
.
