Before your hint came, I used the force method. I deleted the folder with the STM32CudeIDE installation (well, I lost the link to the uninstaller) and the new one installed (v1.5.0), then the update to v1.5.1. And now it works!

I confirm the same problem. In my case: Windows 10, upgrade from v1.5.0, project imported from file system, no "dark theme" (Enable theming - off)BTW Is it possible to withdraw the broken version from the update center to avoid frustration of unaware...