I have to repair a smashed D/G window in an unoccupied house ...
Thinking to replace the panel with a double thickness of 1/2" ply packed out to what I assume is likely 28mm thickness
Bodgier method just screw the ply to the frame from outside, but then the frame would need repair/replace later.
Then slightly longer term either replace glazing panel, or use a 28mm PVC infill panel ... I'd use that now if I though I could collect one rather than have to mail order?