More work on calibrating DSLR photometry in their native systems (more-or-less) has appeared on tonight's astro-ph by Carrasco et al:
https://arxiv.org/abs/2303.14147
Photometric Catalogue for Space and Ground Night-Time Remote-Sensing Calibration: RGB Synthetic Photometry from Gaia DR3 Spectrophotometry
...where the results are derived from the GAIA3 spectrophotometry. Looks as though the scatter is still in the 0.03 - 0.05 mag range, and a bit wiggly. Of course one would want to do the transformations of one's particular set-up in any case. Figure 1 of the paper is a good display of the three very wide GAIA passbands in comparison to the adopted BGR for digital cameras.
It looks to me (again) as though the nominal DSLR blue would transform with small color terms to Sloan g, green is a fair match to Johnson V, and red goes to Sloan r. The astronomical V and g,r are far better defined than what's described in this paper, so I would want to at least try those transformations before anything else.
\Brian