Affiinity Designer supports document export to Adobe Illustrator's AI format by default, thus can be used to achieve afdesign to ai conversion, i.e. export of Affinity Designer documents (.afdesign) as Illustrator graphic file (.ai).
Considering we haven't found any other programs that would support .afdesign files, using the original software seems to be the only viable option to convert afdesign to ai.
Updated: June 8, 2023