1. I have an M30S++ and its control board is damaged. It is not connecting to network. The original board has code CB6_V10_V1.3. I would like to know if CB4_V10 board is compatible with the M30S++?

That's compatible.

2. Are control board models the same for different types of miners?

Regarding types of control boards, they are as follows: air cooling miners CB6_V10; hydro-cooling miners CB6_V5; and immersion-cooling miners CB6_V7.

3. Is it possible for me to buy a single hashboard for my miner?

We don't have any hashboard to be sold. If your hashboard is broken, you need to send it for repair.