The main evidence for the lab leak theory is:

One key part of the lab leak theory has centred on the Wuhan Institute of Virology's (WIV) decision to take offline its gene sequence and sample databases in 2019.

When asked about this decision, Yuan Zhiming, professor at WIV and the director of its National Biosafety Laboratory, told reporters that at present the databases were only shared internally due to cyber attack concerns.