C++20 I would find difficult, we are in the process of updating the toolchain in 1.13 to use GCC9, which brings C++17.
Using GCC10 has side effects and quite a few things break, so for the moment GCC9 is the highest we can do.
You can already build these if you use “moddwarf-new” as target in mod-plugin-builder.
The binaries won’t load in units running 1.12 or lower though.
If you are interested I can share an early build with the updated toolchain.