...The theoratical ones of them mainly talked about scales, intervals, chords, modes, and so on...
I can just imagine it. Endless scales and modes. Charts for each one on different tonics. Charts for matching scales to chords, etc. etc.
I think you might find you beginning theory efforts easier if you think in terms of two principle broad realms: general first terminology and notation, and second relative relationships.
The first is things like time signatures and note values, key signatures, interval names and chord spelling. Basically objective stuff you need to know to talk about music with some precision.
The second part is about understanding musical movement in relative terms. So instead of specific chords like
F7 B♭m, etc. you think of
V7 i the dominant and tonic chords of any key, root change by descending fifth,
G7 adds a minor seventh to a
G major triad, or that minor seventh is added by dropping the root a whole step,
Cm is just a change to the third of a
C major triad, etc. etc. You eventually think/see/hear/finger mostly as interval changes. Root changes by descending fifth, not
7, the seventh of the dominant seventh chord falls a step to the third of the tonic triad, etc. etc.
...I started to find it boring to play without understanding ... After some time I started to find it boring to play without understanding what I'm playing.
One of the most practical things you can do to alleviate that boredom and immediately start learning patterns through actual playing is transpose the songs you already know through all keys.
Guitar presents a particular conundrum when it comes to transposing. Some transpositions are trivially easy on guitar, because you can just slide up/down the neck one fret at a time. Don't transpose your songs that way. Instead transpose by fifths and fourths.
Obviously this will first seem like just learning new fingerings, but when transposing songs pay attention to the interval relationships and which notes/strings are which chord members/scale degrees. Eventually there will be a merging of interval knowledge on the fretboard and common musical patterns. Theory gives you terminology to talk about these relationships and significant patterns.
Transposing is a fast track to this knowledge, because instead of thinking specific chords like
G7 Cm transposes to
F7 B♭m, your theoretical understand of what that progression is in relative terms is more like this: take any bass tone (you don't even need to give it a pitch letter name), play a major third and minor third above that bass (you don't need to know what the letters are), now move the bass down a perfect fifth or up a perfect fourth, and move the third up a half step, move the seventh down a whole step, as a bonus if I want to change the mode of that progression from minor to major the seventh moves down a half step rather than whole step.
It's very, very wordy to say, but it should become second nature to play. When you can play it and can name all the parts, all the relative relationships, that's your performance "muscle memory" enlighten by theory so you will be "understanding what [you're] playing."