I discovered that the dino extension which pulls in libnice and libsoup, namely /usr/local/lib/dino/plugins/ice.so, is not strictly necessary for dino to function well.
It seems it's gssdp(12) that pulls in libsoup(2), gssdp16 would be required to change to libsoup3 (and gtk4), but this would no doubt require updating gupnp*...
..which is going to need doing at some point.