itch.io

You are aware of Dialogic? It's a visual dialogue builder specifically created to create (for example) visual novels. Version 1.5 works with Godot 3.x. Version 2 is still in alpha and works with Godot 4.x. Easy to use.

https://github.com/coppolaemilio/dialogic

Ah sorry - I only now noticed that the overview page mentions that anti-aliasing is allowed. :-)

Answering my own question: yes, it is allowed.

Compare these two tiles:

The left one uses anti-aliased edges, the right one is aliased. Technically the left one is not 1bit, but the rules mention "The same color with different alpha channels is not considered separate colors." Anti-aliasing can be saved via the alpha channel, thereby ensuring only 1 colour is used.