How can I automatically lock my screen when not in use?
By default, your device will auto-lock after 30 seconds of inactivity. You can modify this by going to Settings > 'Display & Brightness' > 'Auto Screen Off,' then adjusting the time from 15 seconds up to 30 minutes (Page 54).
From the official Realme Rmx3997 C65 5G 128gb Smartphone manual, page 54
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