So, Apple decides to make their own 5G cellular modem. Now, apart from Baseband, some of the RF in the cellular is hard (modulators with low power consumption, Envelope trackers, diplexers, duplexers). Some of these were designed by Qualcomm and some from Avago (Broadcom got acquired by Avago and renamed to Broadcom), Skyworks, Analog Devices, etc. So it is not surprising that Apple wants Broadcom's help for next few years until when Apple decides to again vertically integrate and make those components as well ( but they may decide it is not that cost competitive to do do).

The hardest part was Qualcomm's cost and paying them FOB royalties (which got capped at some point by DOJ/FTC involvement).