If you'd ever get the raw data, you can use RTKLIB* for RTK/PPK. Ublox chips stream the raw data, if you configure it to do so.
Nowadays, with dual-band modules, it's no longer necessary nor advantageous to use an external RTKLIB, as the sufficiently precise dual band modules all have RTK integrated i.e. you don't even get decent dual-band GNSS receivers that output raw data but don't have integrated RTK like in ublox M8 times, so there's nothing to be saved by using RTKLIB with available dual-band GNSS modules. And it's not practicable to do dual-band with two single-band modules because you wouldn't get their time references synchronized to a sufficient level for dual-band RTK iirc.
The problem is that the dual-band modules (F9 and such) are - for lack of competition and at least for now and the foreseeable future - waaay overpriced, especially since you need two of them (rover + base) to reach centimeter precision… hence the question about the possibility of doing it with a SDR instead.