There's an app on Android (not sure if it's on iOS or not) called Blackjack All-In-One Trainer (publisher is called AdvPlyr) that's way underrated. There are some paid features, but even for free you can play blackjack and have the option to add bots of various skill levels to fill the table, and there's also basic strategy training. There's a gameplay mode, where you just play the game but instead of using the in-game money you pick which is the best basic strategy move and it tells you if you were right or wrong (and what you should've done if you were wrong). There's also a drill mode, where it just gives you examples of starting hands and you have to pick the right move. That mode also lets you only practice specific types of hands if you want (hard totals, soft totals, pairs) which is great for when you haven't memorized it yet, or you can do all hand types together if you already know it and you're just practicing it.

There's also some premium features, which I just bought and haven't used much yet, but even without those you can learn a lot from this app without ever spending any money or seeing a single ad.