Hello Mirek,
Since the Vulnerabilities Dashboard results are displayed from a Database, the way that they are displayed can't be modified.
Also, for the other Dashboards, there is no option to modify the maximum number of rows displayed.
However, you can modify the maximum rows displayed on the Discover tool that is on the OpenSearch Dashboards on the three-lined menu in the top left corner:

To do it you should access Stack Management on the same Menu:

Then you should go to Advanced Settings, search for "number of rows" on the search box, and modify the Number of Rows on any number you want:

Now when you enter the Discovery section the maximum rows are the ones established on that setting:

From there you should be able to add or remove columns by selecting from the left column the fields that you want to display, as shown in this example:

Just a note on Vulnerabilities, you won't be able to see them in Discover but you will be able to see the alerts that these Vulnerabilities triggered.
If you have any further questions please don't hesitate to ask
Ezequiel