Automatic 2-sided printing is a standard feature.
For Mac: Ensure you have selected the correct printer driver in your print dialog. The HL-L2350DW supports macOS 10.8.x or greater. In the print dialog, look for a 'Layout', 'Finishing', or 'Duplex' menu. Select 'Two-Sided' or 'Duplex Printing'. The printer will handle the flipping automatically.
If automatic duplex fails for a specific media type (like heavy paper or labels), use Manual 2-sided printing. The driver will prompt you to reinsert the paper after the first side prints.
Note: The print speed for 2-sided (A4) is up to 15 sides per minute (7.5 sheets per minute).