Admittedly, once children become teenagers they are expected to be able to read a good amount of everyday kanji words and the use of furigana falls away apart from for unusual readings or less common words, and pretty much entirely for texts aimed at adults. Still, if you're content with quite simple content you can pick up a wonderful amount of language by osmosis with the helping hand of furigana.
So a Kanji that might be accompanied by furigana in a shounen manga (geared to kids) typically won't be accompanied by it in a seinen novel (geared towards young adults). Needless to say, adults don't necessarily want to read doraemon (a kids series) as beginner Japanese learners.
https://en.wikipedia.org/wiki/Radical_(Chinese_characters)
https://en.wikipedia.org/wiki/Chinese_character_classificati...
Also, in the Japanese case, they were borrowed from Chinese centuries ago and commonly given one pronunciation based on what the Chinese word sounded like to Japanese people at that time, and another based on the Japanese translation of the Chinese word.
https://en.wikipedia.org/wiki/Kanji#Readings
So yes, all of this is super-meaningful at an etymological level, but not transparent or reliable, and even trickier with Japanese rather than Chinese, because extra layers like kunyomi were added on top.
That being said, the meaning (or meanings...) of a kanji cannot be derived from its parts, just like the meaning of an English word cannot be derived from the letters that appear in it.
Also, as a rule, the same character will be read differently in different contexts. E.g. 生きる _i_kiru "to live", 生まれる _uma_reru "to be born", 学生 gaku_sei_ "student".
There are anki flashcard (spaced repetition) decks that can help drill the kanji into your head.
Finding accessible reading material is challenging especially at the absolute beginner stage.
In my japanese study I make sure I flashcard kanji every day. Without 300+ memorized reading even kids stuff will be hard.
EDIT: Just saw that you are 4 years into studying. That is a bit demoralizing for me that you still can't read adult level stuff. I can only read stuff along the level of "Ayako rides the train", etc.
I suspect that people who grew up with a non-alphabetic script have better "geometry abstraction capabilities" trained into their brains that would make them noticeably more performant in a test involving fantasy glyph memorization/reidentification.
Kanji make it possible to sometimes guess the meaning and pronunciation of a completely unfamiliar word, but even in those cases it's just a guess. You can never be certain. And in fact, since you can't be certain, it means you need an entirely separate type of dictionary to look up these words, a reverse-kanji dictionary where characters are categorized variously by the number of lines, the presence of certain components, and other schemes of native and non-native invention. This is because you don't have a name for the word you're looking at, whereas in almost every other language, the "spelling" of the word is the name.
About four years into Japanese, the same point where in my Spanish studies I was picking up Don Quixote and enjoying it, I was struggling to cope with young adult fiction. No, I was completely defeated by it. Every page was a slog and it was impossible to progress without turning it into a study session where I looked up the pronunciation of every single unfamiliar word and repeatedly practiced writing unfamiliar characters.
At some point it becomes simply impossible to progress without active, intentional study. The so-called "osmosis" hits a hard asymptote and it's because of kanji. Reading fiction for 12 year olds means pencil, paper, and two dictionaries to decipher it. Or it used to; I guess mobile apps that can OCR the text and look up words have made this process vastly easier for younger learners.
The article is paywalled so mea culpa if this point is addressed in there.