Using only a subset of RGB matrix effects

keymap.c

#include QMK_KEYBOARD_H

uint8_t rgb_matrix_effects[] = {
    RGB_MATRIX_NONE,
    RGB_MATRIX_SOLID_COLOR,
    RGB_MATRIX_BAND_VAL,
    RGB_MATRIX_JELLYBEAN_RAINDROPS
};
uint8_t current_rgb_matrix_effect_index = 0;

enum custom_keycodes {
    RGB_NXT = SAFE_RANGE
};

const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
    // Assign RGB_NXT to one of the keys in your keymap
};

void matrix_init_user(void) {
    rgb_matrix_mode(rgb_matrix_effects[current_rgb_matrix_effect_index]);
}

void increment_current_rgb_matrix_effect_index() {
    current_rgb_matrix_effect_index++;

    uint8_t effect_count = sizeof(rgb_matrix_effects) / sizeof(uint8_t);
    if (current_rgb_matrix_effect_index >= effect_count) {
        current_rgb_matrix_effect_index = 0;
    }
}

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
    if (record->event.pressed) {
        switch (keycode) {
            case RGB_NXT:
                increment_current_rgb_matrix_effect_index();
                rgb_matrix_mode(rgb_matrix_effects[current_rgb_matrix_effect_index]);
                return false;
        }
    }
}