Help, I’m trying to work on a low ish resolution video 112x120, when I import stills shotcut seems to interpolate it, softening the edged of the pixels, whereas I need them to stay sharp and not bleed into the neighbours. I’ve set the project to the same 112x120 resolution, set interpolation to nearest neighbour, tried different images in different formats, .png, .jpg, .webp, but its still bluring the image.
You are not experiencing scaling interpolation directly but rather indirectly through sub-sampled chroma. Nearly all video uses sub-sampled chroma.
If you use File > Export Frame… the image is coming from the player, and the player always uses sub-sampled chroma to reduce the data transfer over the PCI bus to a GPU or video card. Then, the sub-sampled chroma is up-sampled to make a RGB image. One way to remedy this is to use the Export panel with a preset from the alpha or stills category. These ask the engine to use RGB(A) for processing. Of course, this will only work if your video is RGB(A) or YUV 4:4:4, but I do not know what you are using.
Also, please be aware there are some filters that only process in Y’CbCr (aka YUV) sub-sampled chroma, but that is rare. There is a list in this reply.