Hi RickiPadCaricaturist,
Welcome to Affinity Forums :)
You didn't specify which app you are using (Designer or Photo). In Designer (Draw Persona only) make sure the Controller dropdown is set to Pressure or Automatic in the context toolbar.
In Affinity Photo and Designer (in Pixel Persona) the pressure is controlled per brush. Some brushes are already set to use pressure while others may require changes (double-click on a brush or press the white menu icon on the top right of the brushes panel to edit brush settings) - check the Dynamics tab.
There's also an option to Force pressure to control size of a brush in the context toolbar on the right of the More button.
RickiPadCaricaturist reacted to MEB in Pressure