I had a similar (if not the same) issue. I had imported a project with mbed-cli, and exported to Keil uvision, and opened it in uVision 5. When I tried to debug, it didn't know what to do, and couldn't find the flash algorithms.
I had to [1] fix the target (set it to the proper LPC4088 chip in project properties, Device tab), and [2] choose the debugger (project properties, Debug tab, "Use" radio button should be selected, and I chose "CMSIS-DAP Debuger" from the drop-down box). Then it worked for me.