Yes, you can use different learning rates for Actor and Critic by specifying them individually when setting up your training options for DDPG agent. Here is a simple code snippet to achieve this:
actorOptimizerOptions = rlOptimizerOptions(LearnRate=1e-1)
criticOptimizerOptions = rlOptimizerOptions(LearnRate=1e-2)
opt = rlDDPGAgentOptions('ActorOptimizerOptions',actorOptimizerOptions,'CriticOptimizerOptions',criticOptimizerOptions)
Refer to this documentation page for more information on creating an object for DDPG agent: https://www.mathworks.com/help/reinforcement-learning/ref/rl.option.rlddpgagentoptions.html
