There was a study published by the University of Exeter in 2021 that showed the following:

rsfMRI revealed stronger connectivity between the visual–occipital network and several prefrontal regions (BAs 9, 10, 11) in the hyperphantasic group when compared with the aphantasic group

Here is a link to the paper: https://academic.oup.com/cercorcomms/article/2/2/tgab035/626...

So there does appear to be a way to potentially test for aphantasia that requires no self-reporting, just an attempt to visualize.