Hi,
today I downloaded the BaseBox from the link above and gave it a try on the P4-4G. As Hans mentioned it is build/linked against Munt but the libs are no longer part of the official Raspbian 64bit. So I loaded
mt32emu from GitHub and it build fine. After that I also had to install the SDL2_net package from the repository before I culd run basebox. I would suggest to remove Munt from the dependencies as Roland MT-32 emulation isn't need for GEOS and when running DOS games it requires the original ROMs that are not freely available.
The DOS
Dhrystone benchmark I run gave me a score of ~26. This is less than the includes DOSBox (~29) and compares to the CPU speed of an IBM 486DX2-50. With the optimized build of DOSBox that ships with Pi/GEOS I get the same speed on a Pi3. I assume the dynacore still needs some optimization on the arm64 architecture. It is also possible that the new build system does not choose the right parameters...
Thomas