There are so many avenues to go down here but the Theory concepts that have personally helped my own playing are :
1. Knowing The Notes in your Major Scales off by heart **verbally* :
If you know each note name in your Major Scales this way (without your instrument) then you can think about what's happening on your instrument way easier - All the information is internalised in your head etc - Youtube: 'Memorizing Major Scales - Rowan J Parker - for an excellent and easy way to do this!
2. Intervals - Learn what they are, how to form them into chords, how to recognise them when you hear them - Rick Beato Ear training videos will be great for this.
3. Learning your Major & Minor Triads all over the neck in all inversions:
I uploaded a PDF with all of these on a previous thread (I'll try and find it and link it) - these have been the rosetta stone in unlocking my playing and not getting trapped in boxed scale shapes or big arpeggio structures (nothing wrong with scale shapes or sweep arpeggios - triads are in smaller pockets and allow you to make more authentic decisions because you're commiting to less notes in the moment - if that makes sense - if not you'll see what I mean eventually) Check out Tomo Fujita on YouTube - great simple explanations, best to be patient with his English cause the guy is amazing
4. Learn how a Major Key works:
If you really understand how Scales form Keys and the Chord Scale relationship works (YouTube Rick Beato Basics Of Music Theory for the most structured version of this info) things will really begin to make sense for you on your instrument.
The reason I picked these three topics:
1. Knowing your Major Scales will help you learn your Major Keys
2. Intervals will help you when figuring out songs or trying to put what you hear in your head onto your fretboard
3. Triads will give you a simple way of visualising the neck to get interesting melodies
4. Knowing a Major Key will help you understand how most songs work - You'll be able to understand Minor Keys off of the back of this info. The chord scale relationship will help with how chords are constructed too.
A lot of this stuff will be best studied with a notepad rather than a guitar, but it really is powerful stuff when paired with your instrument
Hope this gives you some stuff to get stuck into!