Do you have to study chess theory?

No! I just consulted the I Ching, Tarot cards and
Zoltan the fortune teller for 30 years. Kept me solidly superglued in the 1600-1700 rating range
for those 30 years. If you want to remain a stagnant ratings patzer who is a masochist who enjoys losing, just ignore chess theory. OR do the hard mental work that it takes to progress SLOWLY. For most of us the saying - "There's only 2 speeds to learning chess and improving, slow and stop, if you dont like the first one, youll hate the second one." is true. Took ONLY 30 years to concede to the fact that, in most positions, but certainly not all, bishops are superior to knights.
Joking aside, I've played "The Game Of Kings" for 58 years and understanding chess theory
is the tool you can depend on, that move memorization, tactical prowess, cannot give you
in unfamiliar positions where you ask yourself
"OK! What do I do?" I strongly suggest playing 960 Fischer Random as your play often is made by thinking in chess theory terms, such as control the center, develop knights before bishops, chain up your pawns, overprotect, Rooks on open files, etc . But what would a 63 year old buzzard
who has played chess for 58 years and rated 2000+ on Lichess know!?

Theoretically, chess is more than mere memory ... or is it ?

It is much more than memory. Theory can only carry you till move 15. After that, it is all up to you and how you pave the game. Sure, there are many positions you have to memorize, like theoretical endgames and openings, but it is all shaped in the middle game. There is no memorization in the middle game normally and hence you have to use everything you have learned.

Openings do not have to be studied in detail until one is 1800 or so. Midgame tactics is the difference between a 1400 woodpusher like me and a strong 1800 tournament player. Fortunately, there is this: https://lichess.org/training/mateIn1 Fun little mating puzzles. I play them to relax. Once one gets good in them, it’s time to move up to https://lichess.org/training/mateIn2 Once one is good at that, then just look at tactics in general, e.g. https://lichess.org/training/

Right now, I’m having a lot of fun with the https://lichess.org/training/mateIn2 puzzles.

Another thing: Composed puzzles do not improve one’s Chess playing ability. The positions should be from real Chess games, as they are with Lichess’s puzzles.

Never say that you have worked.
If you fail you have an excuse, if you win you are a genius.

I'm too honest ... I have worked at Chess ... Win Lose or Draw

@Sholmes49 said in #35:

Never say that you have worked.
If you fail you have an excuse, if you win you are a genius.
Students can say that too. I got an A without reading at home. I'm a Genius!