By default, any Column layers in your designs will be set to stack on mobile (unless you’re using a preset component where this is already turned off prior to match its intent).

You can change this behavior on mobile by clicking on any Row layer, then clicking the Settings layer in the plugin header, and toggling the Stack Columns in this Row toggle option on or off.

If you’re using a more than 2 Column layers in your Row, you may want to consider keeping them set as stacked, otherwise the content inside of them can become very narrow and small on smaller mobile device screens.