So this is super bizarre, but I found a way to launch the Sisi client without the launcher using cmd.exe via wine:
wine cmd.exe
.\exefile.exe /server:singularity /ssoToken=<> /refreshToken=<> /settingsprofile=Default /machineHash=<> /language=en /verbose
The client launches but doesn’t connect to Sisi due to a problem with formatting the ssoToken. This means the issue should between the launcher and the client, not with the client itself. Will continue debugging but I have to take a break now.