OC4BAv5 was developed before MSFS was released and has airplane drivers and scripts for the PMDG 737 NGX and PMDG NGXu airplanes to be used with the Prepar3D simulator.
Oi4FS was developed to have ONE main program that works with both Prepar3D and MSFS. It comes with airplane drivers for airplanes that use the G1000 NGXi avionics, MS/ASOBO's B747 and B787, MS/ASOBO CJ4, FWB A320NX and users of Oi4FS can buy add-on drivers for the AeroSoft CRJ, Leonardo "Maddog" MD82 and PMDG 737 for MSFS to be used with Oi4FS.
Both OC4BAv5 and Oi4FS can be seen as shell or main program that creates airplane configurations and start airplane drivers. Oi4FS is making OC4BAv5 obsolete, so I am now only using Oi4FS. Oi4FS has also an Autostart function that will automatically start up the correct airplane driver based on which airplane you fly in Prepar3D or MSFS.
As per 2022-06-26 and the PMDG 737 update v3.0.24 the OCP4NGXu driver that come with OC4BAv5 will not work with the PMDG 737 in MSFS.
So to use your Opencockpits modules when flying the PMDG 737 in MSFS you will need the Oi4FS add-on driver PMDG 737 for MSFS.
Hope this clarifies things for you.