MIDI (Musical Instrument Digital Interface) is a protocol for communication between electronic musical instruments, computers, and other related devices. It is a digital interface that transmits data about notes, timing, and other control information, but does not transmit audio signals.
A line-in, on the other hand, is an audio input port on a computer or other audio device that accepts analog audio signals from a source such as a microphone, guitar, or mixer. Line-in ports typically use a 3.5mm TRS (Tip-Ring-Sleeve) connector.
Therefore, a MIDI adapter cannot be used as a line-in input.