So, distcc lets you compile C or C++ applications on machines (or nodes) over the network, sharing the workload. But for the life of me I can't make it work from within a distrobox on the Steam Deck.
So I tried icecream (icecc), which is made by the SuSE folks. Not only does it work with distrobox, but it requires less configuration (just enable some systemd services or run the daemon) and everything Just Works. Having three machines + compiling projects with the --parallel flag should make even Qt compile quickly.