I've installed C++ Builder 10.3.3 few days ago on my secondary PC. Not the newest machine, running Windows 7 64-bit, but still quite capable with quad core CPU and GT430 graphics card. C++ Builder was pretty much useless on it though:
Once new project was created or old project was opened most of the GUI was either frozen or refreshing with huge delay. At the same time bds.exe was using 100% time of one of the cores. What is weird is that once C++ Builder window width was reduced to about 1100 pixels the problem was gone. Still, working with window width reduced to half of screen width would be very painful.
Solution is easy to find: disable support for themes in IDE (HKEY_CURRENT_USER\Software\Embarcadero\BDS\20.0\Theme\Enabled, set to 0):
