For some odd reason when you select the text tool in Affinity Photo you are offered a fill color but there is no stroke color which is very strange.
You can add a stroke / outline by using a workaround, with the type selected, select the rectangle tool or one of the other shape tools and then you will see the required field you can then set the color as well as the size (it is next to the color) and also add into the mix, a dash line style as well as pressure to give your type a more hand drawn look.
You can set the fill to none via the fill panel by clicking it and going to the diagonal cross mark along the top of the panel or go to the swatches and selecting the nil entry.
You can create a large edge by increasing the stroke size. You can set it to any color, set the dash style etc. If you are also using Designer, you can also go and edit in that via the file menu and add additional edges to your path by using the appearance panel.
You can also modify it further by applying effects to it such as blurs or perhaps combining it with different backgrounds or the same characters with a large size width or perhaps adding layer effects to the characters. https://youtu.be/gbTsooaAl28
There is also an additional outline feature in layer styles (click the fx at the bottom of the layers panel) and you can combine that with the existing one. It is not as useful as the powerful appearance panel in Affinity Designer though especially as you cannot add multiple entries to it (something that can be done in other applications) https://youtu.be/vGVit8uyWaw
To extend it even further, you can use the powerful contour feature found in Designer and if you have both applications, you can seamlessly move between the apps via the file menu edit commands and add contours to your artwork and they can also be added multiple times by using combinations of bake appearance. https://youtu.be/ZeZPtq4cuLw