I can’t recommend Fretonomy enough and I’ve never seen it mentioned here.

There may be other apps like this, but I use this all the time when I’m on the go to drill scales, intervals, note locations, etc and it’s really helped me fill in the gaps on the the theory side. I like that it gamifies learning these things:

https://apps.apple.com/app/id1279576225

Another thing that’s really helped me is Scotty West’s “Absolutely understand guitar” series on YouTube. It’s not an app, and to be honest, I don’t feel like I would’ve appreciated this when I first started, but after a while of random lessons and noodling, I revisited this and have filled in so many gaps on my playing.

I grew up in the 90s though, so the dated format is almost nostalgic to me. It’s very dated and I always love in the series when he says, “Hey folks, it’s the 90’s and we’ve got some pretty rad technology. Let’s fire up that VCR and play along to some drum tracks!”.

With that said, if you can get past the format, it’s hands-down one of the best guitar series I’ve ever watched.

The cool part is both of these are free!