Re: How to fix the gap in the corner wall where it meets the window
Welcome to the Bunnings Workshop community @aetherah. It's wonderful to have you join us, and many thanks for your question about repairing gaps.
I'd suggest you start by clearing out any fragile material with a Stanley knife or flat head screwdriver. I can see the curved lower portion of paint has delaminated from the wall, so chip it away and remove it. Once you've cleared out the area, you might like to give the area a quick sand with 120grit sandpaper to ensure the 90-degree corner is nice and crisp.
You can then mix up a small amount of builder's bog to fill the void and return a slight cove to the internal corner at the same time. A paddle pop stick might be useful for this. Avoid applying too much bog to the area. Better to do a few light coats than one excessive heavy coat, which will be pretty hard to sand back.
Once the bog is dry, sand it back with 240grit sandpaper, removing any high spots whilst smoothing out the transition between surfaces. Once you've given the area a sand, apply some undercoat and then, once dry, the enamel topcoat of your choice.