I just downloaded and installed 0ad on Developer Build #1 of MacOS 10.15 Catalina. As in 10.14 Mojave, the game immediately pops up with "unknown developer." Right-clicking the icon and choosing "Open" appears with the standard "Open / Cancel" options, which have not changed.
OpenGL is deprecated according to Apple documentation, but the game appears to still load and play as normal. OpenAL is also now deprecated, but sound does play without a problem.
For now, it appears, 0ad is in the clear. However, it is perhaps best to get 0ad notarized, perhaps on the Mac App Store, and to develop for Vulkan while supporting MacOS using MoltenVK.