Thanks for your interest in Bitnami solutions. You have tagged your case with "WordPress Multisite" buy you are following the WordPress Production Ready documentation. I assume that you actually have launched a WordPress Production Ready template instead.
For installing new plugins, you can use the "wp-cli", but as you can see below, for updating and installing plugins you should be able to directly update them from the WordPress admin panel as it is explained in the second part of this section:
Could you send us a screenshot of the Plugins section of your admin panel to check which can be the issue you are having updating plugins from there?
We have a Support Tool that will gather relevant information for us to analyze your configuration and logs. Could you please execute it on the machine where the stack is running by following the steps described in the guide below?
How to Run the Bitnami Support Tool3
Please note that you need to paste the code ID that is shown at the end.
If you are still running into issues, don't hesitate to post here your questions. We're happy to help!