If you are looking for more of an app experience I recommend Lingo Deer. You will probably go over material you already know, but will also get exposure to new material. Other have recommended Human Japanese. I have not tried it yet, but those who have enjoyed it.
If you are looking for books you can take a look at Tae Kim. If you want a slower book series that provides you with random details that may or may not be useful (but usually very interesting if you want to know the history behind the language or other bits of knowledge) you can go with the Japanese From Zero series. I believe 4 books go over the similar material as in Genki 1 and 2 (although I don’t know personally and no one has confirmed that it gets this far). JFZ does offer some videos and it looks like they have some online learning options. I also enjoy the Attain Corp videos. I have only watched the N5 and some of the N4 videos. If you prefer to watch videos it’s an option. There are also some YouTube videos out there, but they aren’t always in order of what you should learn.
Honestly though Genki is one of the better textbooks. They do have a website and app. I haven’t used these yet, but it’s worth looking into if you decide to stick with Genki. The reality is that learning Japanese is tedious and in the middle it can get a bit dull until you reach the level where you can understand more native material better.
Alternatively you might want to consider taking classes. If there’s no classes near you then you can look into online tutors. I used to think it was so expensive and while it can add up it can definitely be worth the money.
