This is a space of vector valued Siegel modular forms with real representation $\mathrm{Det}^{ 20}\otimes\mathrm{Sym}^{ 4 }$. The following table gives the dimensions of various subspaces of $M_{20, 4}(\mathrm{Sp}(4, \mathbb{Z}))$.
Total | 8 |
Non cusp | 2 |
Cusp | 6 |