Hi petersirka,
Welcome to Affinity Forums
Yes, if you enable the (automatic) grid (menu View ▸ Show Grid) and Snapping (menu View ▸ Snapping Manager - make sure Snap to grid is enabled) Affinity will snap to half pixels letting you position the 1px lines perfectly aligned with the pixel grid (no antialiasing). You will need to zoom in considerably to see the grid as a 1x1px grid.
Seems recent changes here (OpenGL and Metal renderers) have made this more difficult to work with. It's necessary to zoom in way more than previously to display a 1x1px grid. I'm logging these issues.
petersirka reacted to MEB in Affinity Photo: Pen tool 1px stroke width