Someone introduced me to an app called Yousician, which is an app for learning certain instruments and singing. It “gamifies” the practice to be a bit like guitar hero, which is the way it is able to provide you feedback without an actual person hearing you sing and offering feedback. The game also makes it a bit more fun to do on your own.
Don’t do the paid version for singing. The number of singing lessons the app offers is really pretty limited. Just use the free version, sit through the “pay for premium!” voice ads that happen every so often, and continue until you reach the time limit for the day.
The value is in the video tutorials that explain techniques, which are then followed by game-like practice that gives you immediate feedback on your pitch and timing, so that when you then practice songs on your own you begin to have an idea of what to work on and what to aim for in your practice. I’ve gone through the singing lessons. I’ve seen a significant immediate improvement in my ability to sing on key. I can more accurately hear and match notes. More significantly, I also feel like I have ways of approaching singing that I can use to keep improving my voice on my own (at least as much as I can without more technical training).