This plugin adds a widget which allows to fetch content of external WordPress installations. Basically it can be used to fetch anything which returns JSON, if the JSON contains at least entries named "link" and "title".
Copy this plugin to your WordPress plugins folder, activate it and check the widgets section of your theme. Add the widget to your sidebar, set a title and enter the URL to the WordPress REST interface of your external server. Optionally set the maximum length applied to each entry returned by your external server.
See the WordPress REST API at https://developer.wordpress.org/rest-api/reference/ for details.