Create some characters for your Affinity Photo text brush. This can be in any font as well as in any color (I would recommend something like green or blue) and set the font size to about 100pt or something unless you want super small writing. You can add the words via the artistic text tool found in the tools panel. You can create the design with no fill and a stroke of 10pt or 20pt. Or perhaps create multiple copies of the object with different color fills / strokes. Or perhaps have the same design duplicated and some of the objects blurred or distorted by the various filters such as deform and twirl. Or perhaps add styles / layer effects to the characters. Perhaps have letters in different sizes and different spacings and angles as well as different fonts.
Once you have added the artwork, go to the layer menu and rasterize as the words need to be converted to pixels (if you want to change the spelling etc then I would recommend your duplicate the layer and just rasterize one of them). If you have multiple layers, you will have to use the merge visible command.
Once you have your rasterized selection, you can go to the brushes panel and right side menu and create from selection at the bottom of the menu and this will be added to the current category. You, of course, create a category for your words.
Once you have this resource, double click it and then edit the settings such as set spacing to low and set size to a decent size and go to the dynamics tab and set rotation to the max and random and set the scattering and set the size to pressure
Set the hue / saturation if you wish to have randomized color artwork. You can set a hue jitter as well as saturation jitter and brightness jitter. To get the maximum range of colors, set the value to 100%.
Apply this preset via paint, clone, mixer etc in the tools panel. You can always re-edit the stroke at any point by double clicking the entry in the panel. If you don't want to lose that setting, you may wish to duplicate the preset before you do an edit as the original settings will be over written.
Create a single character A and then set the font and color and stroke for that design and add a layer effect such as a outer shadow via the fx at the bottom of the panel of layers. You can set the radius and offset and intensity to create a decent shadow effect for that letter. Use the alt / option key and drag to duplicate the letter and then change the character to a B or C or 1 or 2. Change the color as well as the font and stroke as well via the control bar (top left). Position the character on top of the first character and re-size and rotate the design using the bounding box for the artwork. Select all the characters by using the move to drag over all the letters and then go to the layer menu and merge visible command. Go to the panel and right side menu and the new from selection command and you will then see your design now added as a preset in the panel. You can double click the entry and edit the preset such as adding scattering, rotation jitter, spacing, hue and saturation jitter etc. And apply the stroke using paint etc. You can also add into the mix effects such as deform and twirl and blurs to the letters, you can add multiple different letters on top of each other. You can have them faded or use them (they are layers) with blending modes.