FWIW Debian can run on the pinebookpro, which uses a similar soc as the pinephonepro (rk3399 vs. rk3399s). There are a few kernel changes needed, but they might be mainlined by the next LTS.
So I would say maybe in a year or so Debian testing could run on it.
So I would say maybe in a year or so Debian testing could run on it.