The relatively loud "clunk" sound you hear when engaging the first gear on a motorcycle is a normal characteristic of most motorcycles with manual transmissions. It does not necessarily indicate any damage to the transmission.
The reason for the audible noise is the design and operation of the motorcycle's transmission system. When shifting into first gear, the gears are larger and have more teeth engaged compared to the higher gears. This results in a more pronounced and noticeable engagement sound. Additionally, the first gear is often designed with a higher gear ratio to provide more torque and power for starting from a standstill, which can contribute to the sound.
The "clunk" sound is essentially the sound of the gears engaging and meshing together. It is a result of the mechanical components interacting and fitting into place during the shifting process. The noise is more noticeable at lower speeds or when the motorcycle is stationary because there is less ambient noise to mask it.
It's important to note that unless you experience other symptoms such as difficulty shifting gears, grinding, or excessive noise during gear changes, the "clunk" sound itself is generally not indicative of any transmission damage or issues. However, if you have concerns about the operation of your motorcycle's transmission, it's always a good idea to have it checked by a qualified mechanic or technician to ensure everything is functioning properly.