This PIC microcontroller based RC driver is able to control 4 RC Servo by on board
The Pololu 4-Channel RC Servo Multiplexer can be used with standard hobby radio control systems and servo controller to allow easy switching of servo
4-Channel RC Servo Multiplexer
Servo control - Wikipedia
MakerFocus PWM Servo Motor Driver IIC Module 16 Channel PWM Outputs 12 Bit Resolution I2C Compatible with Raspberry Pi 4 3B+ 3B Zero/Zero w/Zero WH
PWM motor and servo controller - I2C 8-channel - PCA9685 - overlay for Feather - Adafruit 2928 Botland - Robotic Shop
RC Servo Controllers
Endurance R/C - WiFi and USB Servo Controllers
Micro Maestro 6-Channel USB Servo Controller (Assembled)
32 Channel Servo Motor Control Board + PS2 Controller + Receiver
LSC-32: Hiwonder 32 Channel Digital Servo Controller with 16M Memory/
Quadruped Robot with SC08A Servo Controller
24-channel dual PWM servo control debugging board for DIY smart robot
Mini Maestro 12-Channel USB Servo Controller (Assembled)