It's simple to solo, just think. That's all it takes.
Learn a bit of theory. Enough so that once you see the chord structure of a song, you can work out the overall pitch. (it's not the first chord).
Then think about the basic melody you want for the song. Try picking that melody out of the major or minor (should the song be in a minor key) scale.
Hey presto there is the beginning of your solo at least.

To play someone else' songs. Learn the key, learn to whistle or hum the solo. When you can it's firmly in your mind. Then find those notes on the fretboard.

The hardest part about it is getting the solo in your mind. Once it's there it's just a matter of time and effort to get it onto the fretboard.

Simple

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No no and no

+1 Niki, that's exactly how I figure out how to get what's in my head to come out of the fretboard. Whistle what I'm imagining and then finding the notes one at a time.

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Tune Low, Play Hard & Floor it!