After the last windows update, a tool (IObit's driver booster) suggested that I have a new GC driver waiting for me. After I updated, the secondary (hdmi) screen was and stayed blank. I completely uninstalled the drivers via windows, running AMDCleanupUtility.exe in C:\Program Files\AMD\CIM\BIN64, then removing the amd folders in C:\Program Files\ and C:\, checking that it did not exist in device manager anymore and restarting and using win10-64bit-radeon-software-adrenalin-edition-18.5.1-may23.exe to reinstall. Both screens show now the same and neither the ad nor the windows display settings program detects the second screen anymore not allowing me to extend the desktop. Using the device troubleshooter resulted in nothing and neither had the Lenovo 'system update' anything to add.
A system restore failed also and I have no idea left what else to try.