The industrial computer has a ground screw on the housing. Is connecting it mandatory, and how is it done correctly?

Yes, connect it. The chassis ground lets noise and surges drain to earth instead of passing through the board, and it improves electrical safety for operators. Correct connection: 1. Use adequately sized wire, as short as possible, from the housing screw to the cabinet PE bar. Flat braided strap drains high-frequency noise better than round wire of the same cross-section. 2. If the mounting plate is part of the earth path, scrape paint at the screw point and use a serrated washer for solid contact. 3. Signal cable shields are usually earthed at one end only, to avoid ground loops that cause noise or current flowing on the shield. Many puzzling faults come from poor earthing: offset touch input, USB or COM ports dropping out, random RS-485 errors, the machine hanging when a drive starts. When you see these, check earthing before suspecting the hardware. Note: the plant's earth electrode must meet the resistance required for the electrical installation.