I have a project for STM32F446 generated by CubeMX.
After changing some pins and re-generated the code, it builds successfully but the debugger settings in the uvoptx file are broken: Keil's debugger cannot connect and shows "unknown target" in debugger settings. But it sees the ST-Link dongle and its serial number.
The solution for me was to restore the uvoptx file from backup. It may be caused by the recent CubeMX update (4.24) or not, I'm not sure.
Another suspicious thing after CubeMX update is that it inserts spaces between components of include path in Keil project (uvprojx). But Keil does not mind...
Hope this may help to others with the debugger issue, I've lost a lot of time today checking all cables, boards etc.