The Styles Pane in Word has been changed again.
Each style is appearing in a panel of its own, decreasing the number of styles that can be displayed.
You can add comments / remarks about this directly on UserVoice in this suggestion.
Here are screen shots from 365 Version 1903.
Compare with screenshots from Word 2013:
I added an extra column in the Word 2013 views. Earlier versions allowed up to four columns in the Styles Pane. Even so, in the no preview view the number of styles viewable in the Style Pane has been dramatically reduced.
These are on a Windows PC. My guess is that this is another effect of multi-platform design. I really prefer the 2013 design and wish there were an option available to use it. I will be sending a link to this page to UserVoice and Feedback.