I can very much relate.
When I was a teenager and learning theory through the RCM curriculum, my particular experience of the way it was taught was extremely rule based, focused on the score, focused on note spellings, with laundry lists of do-nots. Conspicuously missing was any connection to sounded music, the keyboard, the voice. Mysteriously failing to mention references to actual music examples and the composers that paved the way for these "rules." They were just rules to be followed without explanation of why they were there and why music needed to follow them. It was theory by the book, theory for the book, and theory worked out in isolation with the book.
My theory teachers at university changed all that, where we had a music-first perspective of theory. Every theory class in university was filled with sound, the professor playing the piano, playing back recordings of all kinds of music. We were required to sing and play examples at the keyboard (that meant everyone regardless if they were singers or keyboard players). When a theory topic was introduced it was always backed up by real music examples. We would hear the teacher play it, then we would have to sing it to further internalize the concept. Musicianship skills were very tightly integrated into the theory courses, and one would not be able to get through a course by just reading a text book and regurgitating it back on score paper, one had to actually perform these concepts musically. We had to be able to hear and identify these concepts by sound, not just by score analysis. Transcription was a frequent exercise. Out of of a two hour class, maybe 20-30 mins talking about the concept while the rest of the time was devoted to listening, singing, transcribing and working out examples musically.
Making music theory in a music oriented learning approach is what really solidified understanding of how all these rules related to real music.
My suggestion to you is to play and sing through some real music to really understand what it sounds like. Get yourself a hymn book and study the SATB hymns and chorales. Study the Bach chorales. Listen to choirs singing this music.
Don't be afraid to make mistakes because of the "rules." Don't be afraid to forget a rule because there are too many to remember. Write out and play SATB chorales first, then worry about applying rules to them once you have established your flow in writing. Intentionally break rules and observe what it sounds like, it can give you a better understanding why that rule is suggested.
If you don't have a hymn book, start with some online hymn resources such as hymnary.org
IMSLP also has hymn books, here is one
https://imslp.org/wiki/The_English_Hymnal_(Various)Although, having a physical book is easier to browse and work with. You will want to focus on the SATB hymns, because that is closer to what is studied in theory courses.
If you want to become more comfortable with harmony start with real music, not text books. A text book can help you understand the theory better once you have heard and played music.
Topic: I suck at harmony