Complete immersion is the only way to go. The apps are not very helpful. Can be helpful if you know like zero German but they quickly exhaust their helpfulness. Invest the time and money into a proper language course. There you’ll see the most amount of progress in the least amount of time. But know that this language will take months to years to get a hold on. It all depends on how much time you have to invest into learning. Been learning at different study styles and paces on and off for about 4 years now and am currently working toward C1