A lot of the patents needed to implement mobile standards are designated as "standards essential patents", meaning that the party bringing them up the table in the standards committees needs to disclose them and agree to licence them on a FRAND basis to anyone who asks (fair, reasonable and non-discriminatory).

In many cases there are patent pools you can license that cover large areas of the standards, without needing to negotiate each one individually.

Many very fundamental parts of 4G/ 5G are patented and you'll not be able to get your device to work on the network without those patents, so Apple will have licensed those patents under FRAND for their new C1 modem.