Overview
I have updated the Mirador repository with the Text Overlay plugin that supports vertical text.
https://github.com/nakamura196/mirador-integration-textoverlay
References
The original Text Overlay plugin repository is below.
https://github.com/dbmdz/mirador-textoverlay
Demo
You can check the behavior on the following page.
https://nakamura196.github.io/mirador-integration-textoverlay/
Press the “Text visible” button in the upper right to display the text. If it remains in a loading state, try reloading the page.

References
The Text Overlay plugin was added to Mirador 3 using the method introduced in the following article.
Usage Examples
For usage methods of the Text Overlay plugin, please refer to the following article.
Summary
In the future, I would like to fix the bug where the text display remains in a loading state.
I hope this is helpful for applications of IIIF images and text.