Thanks marioroy++ for this present. And happy festivus to all from me as well.
A slight complication: in my linux box the cuda compiler (nvcc) needs some specific gcc versions (for nvcc v 10.1, 10.2, gcc version must be 8). If there are multiple compilers, nvcc must be told where the compiler to use, resides via e.g. --compiler-bindir=/usr/local/gcc84/bin (and make sure that in that dir there are executables or links named gcc,c++,cpp). I found that placing a line (my first and only, I hope, interaction with the Serpent for this year!) '--compiler-bindir=/usr/local/gcc84/bin', in mandel_cuda.py, line 57 (e.g. where the options array is set), compiles your program and yep! it shows spectacularly my holy-grail since the years I was still sucking on my Alma Mater's mamma (at the guts, in the Sun-Sparkstations dungeon).
I have also encountered the problem that pycuda would not install (via pip3 as per your instructions) because it did not know where my cuda-sdk installation was. I solved that with export CPATH=$CPATH:/usr/local/cuda/include; export LIBRARY_PATH=$LIBRARY_PATH:/usr/local/cuda/lib64
bw, bliako