1- The bank buys the house for 100,000, then sells it to you for 120,000.
Here's no problem.
2- The bank lends you 100,000, and you buy the house, or you buy it for you, and it gets back 120,000, and here the loan is riba.
The disposal method is that you do not take money from the bank with the intention of the loan, but with the intention of saving money from the hands of a non-Muslim.
And if the bank is going to buy the house with the agreement between you and him and give it to you, you can take the house with the same intention, and it doesn't hurt you that the bank will take 120, 000 from you