Can the balcony side wall be fixed on the horizontal bar with sandbags?

First of all, according to your description, if there are hollow bricks, you can't fix the horizontal bar. A hollow brick can hang a photo frame with nails at most. Decoration will not put the expansion bolt of the clothes drying rod in the hollow brick, and the hollow brick will not bring stability to the expansion bolt. The main function of hollow brick is heat preservation and sound insulation, not load bearing. The brick surface is only 90 mm thinner than the book-120m. I suggest you install it on the ceiling. The seller of sandbags will tell you that there is a special roof fixing device, which is very strong. Never fix it on the balcony side wall, because the sandbag will swing when it is hit, and the force will greatly exceed its own weight and be uneven, which is prone to danger, such as flying out of the balcony. . . . I wish you success!