Raindrops creation in Affinity Photo ? Open an image or create a new layer and add brush strokes / gradients etc to that. Go to the tools panel and select the ellipse marquee tool and then go to the top left and select the add mode for that.
Apply the tool and hold the shift down and create multiple circular marching ants across the image. Go to the edit menu and use the copy and paste commands to create a new layer (which will contain parts of the underlying image). De-select via the select menu.
Go to the fx at the bottom of the layers panel and click 3D and change the settings as required and likewise the bevel category (see the video for the settings though the end result will depend on the size etc. Once you have your droplets across the image, you can always go and merge them via the layer menu.
You can do all of the above but with patterns. Go to the image and select. Go to the layer menu and create pattern command and you will now see a tile that can be re-sized and rotated. You can also exactly the same as above and add a number of marching ants to the area of the tile. No point in going beyond it though you can use the tool to select the edge as well but the result will be some unusual shape drops in many cases. Copy and paste and that will also become a pattern and they can be modified separately or combined by using both the tile and image. Creates some surreal effects when the alignment of the bubbles etc is different from the original image.