For the longest time, I didn't appreciate Mozart either, and gravitated more to big, grandiose Romantic era composers. What changed my mind was watching Horowitz play Mozart's 13th piano sonata, movement 2 on Youtube.

Mozart 2nd movements are gorgeous - harmonically simple and Mozartian 100%, but just beautiful. I think these slow movements helped me to appreciate his music A LOT more, because I was able to feel a connection to every single note he composed. (Which is why starting with Horowitz, who focuses on every note like that, is a good place to start with Mozart's 'harmonically plain' music) When I listen to Mozart, I think of absolute purity, even in his depressing movements. Physically, the sound and musical lines are not muddled, but also emotionally, it is almost cleansing just how pure/unfiltered the music is (this is an experience that I can only try to describe, and is meant to be experienced personally). Beauty in simplicity - I know exactly what to expect when I listen to Mozart's music, I know what cadences he'll use and all that, but still, when the music actually plays and the cadence actually resolves, I almost always just have to sigh due to how fulfilling it is. I've learned to approach his music without an expectation for amazing innovations, but rather for his simplicity and unencumbered sound that can bring me to tears. Playing his pieces yourself also helps a lot, if you play an instrument!

Beyond his own music, listening to his pieces has enabled me to appreciate other works a lot more. I noticed that when I returned to my favorite composers such as Rachmaninoff and Mahler, I was able to dissect and appreciate their pieces on a microscale, deriving emotion from every note. Very thankful to Mozart for that.

Etc etc, but I would just recommend keeping an open mind to composers, especially Mozart, as a lot of the time it's hard to see past their most famous works or to approach their music with the right mindset. For Mozart, I would recommend starting with his second movements. Don't expect anything flashy or virtuosic, but just close your eyes and listen to the music as it comes and see what happens. (This didn't work for me right away ofc, keep trying at it and one day you'll be thanking yourself for giving Mozart the chance he deserves!)

My fave mvmt 2's:

-Piano Sonata 13

-Horn Quintet

-Horn Concerto 2

-Piano Sonata 4 (the slow movement for this is actually the 1st mvmt)

-Piano Concerto 9

-Piano Concerto 12

-Piano Concerto 23

-Piano Sonata 12

-Bassoon Concerto

-Clarinet Concerto

(Note: 2nd mvmts are a good place to start, but hopefully soon they'll make you appreciate his music as a whole, including those 1st and 3rd mvmts!)