Just Installed 8.6 and same behavior of not starting after the initial splashscreen. I checked the windows event message and looks like the mysql dll failed.
Faulting application name: digikam.exe, version: 8.6.0.0, time stamp: 0x67d47119
Faulting module name: libmysql.dll, version: 8.0.40.0, time stamp: 0x679767b8
Exception code: 0x80000003
Fault offset: 0x000000000006e722
Faulting process id: 0x0x2A30
Faulting application start time: 0x0x1DB99C24DFC1B5A
Faulting application path: C:\Program Files\digiKam\digikam.exe
Faulting module path: C:\Program Files\digiKam\libmysql.dll
Report Id: f1ae5826-6622-4219-a8c7-3dc5f1a9baea
Faulting package full name:
Faulting package-relative application ID: