Silicon Labs is a Bluetooth module manufacturer and solutions provider. Over the years they have created a large number of useful technical notes. They have just created a master list that allows easier access to the notes. Here are some that more general, less proprietary and not specific to Silicon Labs’ modules:
Bluetooth advertising data basics
Throughput with Bluetooth Low Energy technology
Bluetooth advertising using manufacturer specific data
BLE Basics (master/slave, GATT client/server, data RX/TX)
Understanding the Bluetooth Connection Process
Bluetooth Mesh Training resources