Grid view is now the default representation for the records in a portal. To show the records in another way, go to:
Click on the linked records field where you want to show the records as a list
Go to the Views section
Set Layout to either List, Gallery, Kanban, Chart, or Calendar.
At the moment, the Chart view only accepts number and formula field for Y axis.
By default, the mobile view for the portal displays the List layout instead of the Grid, even if you have selected Grid as the preferred layout for a better viewing experience on mobile devices. However, if you still prefer to show the Grid layout, you can change this setting by accessing the portal's settings.