I want to open an account with a financial institution. This account earns interest on the balance by default, but after opening the account, I can turn the earn-interest option off before depositing any money, so no interest is earned on my balance. I just want to make sure if this is okay?

The problem remains with the contract itself: it contains usury (riba). Pay attention to that and see if you have alternative options. If you do not have alternative options, then yes, you can proceed. However, make sure that you turn off the usury/riba elements, do not fall into them, and take extra precautions.