how does dash solve the scaling issues? I heard dash has some extra features compared to bitcoin like masternodes etc, can someone explain the subtle differences especially regarding the scaling debate
The biggest reason why Dash can scale is incentive alignment. Dash splits the block reward between the miners (45%), masternodes (45%) and the treasury (10%).

Masternodes are a special type of node with some extra requirements. In exchange for that, they get paid by the network. Because they get paid, the network can require them to run powerful machines that can handle bigger blocks than what would be possible with volunteer nodes (like what happens with Bitcoin, Bitcoin Cash or Litecoin).

Also, thanks to the masternode layer, Dash is about to release a decentralized API that will allow light wallets to connect to that layer as a class, not an individual (trusted) server. With that, it will be possible to use Dash in a completely trustless way without the need to download the blockchain, reducing the pressure to keep it small because only very specific use cases will require to have your own copy.

There are a few more improvements in the works that will all contribute towards scalability. Arizona State University recently released a paper analyzing Dash scalability:
https://blockchain.asu.edu/block-propagation-applied-to-nakamoto-networks/

As a side note, Dash also has a governance system in place that facilitates decisions around the protocol. That is not technically an advantage towards scalability, but because decisions can be made easily, roadblocks are only temporary. The decisions to go from 1MB blocks to 2MB ones was agreed by the network in less than 48h, saving a lot of time in discussions between parties claiming to represent the best interest of the network but without a real way to prove that.