Yeah, the way the question as posted is a bit confusing.
Add a layer - white or otherwise and it will appear above the (jpeg) image. A chequer pattern implies it is under the jpeg.
Regardless, Adding a layer and it will have an alpha channel. Go into Layer -> Transparency -> Remove Alpha Channel Removing the alpha channel and transparency is removed. Using the eraser tool works but uses the background (BG) colour, so make sure that is white. Of course, painting over in white has the same effect.
screenshot https://i.imgur.com/mR4MSRj.jpg
A better way, Two layers a transparent layer over a white layer, paint on the transparent layer then you do not have to worry about the chequer pattern.
screenshot https://i.imgur.com/EAKm93s.jpg
@gnuimpcub if you can post a screenshot it always helps.
Add a layer - white or otherwise and it will appear above the (jpeg) image. A chequer pattern implies it is under the jpeg.
Regardless, Adding a layer and it will have an alpha channel. Go into Layer -> Transparency -> Remove Alpha Channel Removing the alpha channel and transparency is removed. Using the eraser tool works but uses the background (BG) colour, so make sure that is white. Of course, painting over in white has the same effect.
screenshot https://i.imgur.com/mR4MSRj.jpg
A better way, Two layers a transparent layer over a white layer, paint on the transparent layer then you do not have to worry about the chequer pattern.
screenshot https://i.imgur.com/EAKm93s.jpg
@gnuimpcub if you can post a screenshot it always helps.