Here's the key to improvisation, and it's not easy. It takes real dedicated work.

First, scales, as someone else pointed out, are basically like letters. You don't form words by putting together "ABCDEFG". Arpeggios are what we should put a lot of focus on, much more so than scales, because arpeggios outline the chords that chordal instruments (such as guitar, keys, etc) play, but we do it rhythmically like a drummer. It doesn't stop at arpeggios (there's chromatic approach notes )

Learning arpeggios is the easy part. Even learning all the core arpeggios (major-7, minor-7, dominant-7, half-diminished) inside and out, backwards and forwards, inverted, over multiple octaves - that's going to take a lot of work, but it's still not the most challenging bit.

To truly be able to improvise you have to "speak" in music. What I mean is, you have to be able to hear what's in your head and then execute it on the fly. It's similar to talking to someone. When you are having a conversation you don't have to think about individual letters or words, you have a general idea of what you're going to say and you just say it because talking is so natural. The goal is to get to that point with playing music.

You can kinda fake it when you learn enough patterns, you can tie these patterns together to create interesting solos, but often times that's just sorta flying by the seat of your pants.

It takes a LOT of practice to get there, singing the pitches when you practice arpeggios helps a lot.