LED Strip Button looping code issue

Other Hardware LEDs and Multiplexing
27

so no luck?

I would go for a modification of the state machine to only check for button state when you have completed a cycle

#include <FastLED.h>
#define NUM_LEDS 30
#define DATA_PIN 5
CRGB leds[NUM_LEDS];

const byte buttonPin = 7;

enum : byte {STOPPED, RUNNING, PAUSING} currentState = STOPPED;

const int deltaStep = 5;
const int startingColor = 255;
int colorStep = startingColor;

unsigned long pauseStartTime;
const unsigned long pauseDuration = 1000; // in ms ie 1 second

void fillStrip(byte c) {
  for (byte px = 0; px < NUM_LEDS; px++) leds[px] = CRGB(0, c, 0);
  FastLED.show();
}

void black() {
  FastLED.clear();
  FastLED.show(); // not sure if this is neeed after clear
}

void manageStrip() {
  switch (currentState) {
    case STOPPED:  // we are stopped, if there is one button press, start running
      if (digitalRead(buttonPin) == LOW) {
        colorStep = startingColor;
        currentState = RUNNING;
      }
      break;

    case RUNNING: // run a complete cycle, at the end check for button still pressed
      fillStrip(colorStep);
      colorStep -= deltaStep;
      if (colorStep <= 0) {
        black();
        if (digitalRead(buttonPin) == LOW) { // button is still pressed, pause for a bit
          colorStep = startingColor;
          pauseStartTime = millis();
          currentState = PAUSING;
        } else { // button is no longer pressed, stop
          currentState = STOPPED;
        }
      }
      break;

    case PAUSING:
      if (millis() - pauseStartTime >= pauseDuration) {
        currentState = RUNNING;
      }
      break;
  }
}

void setup() {
  pinMode(buttonPin, INPUT_PULLUP); // wire pin D7 --- button --- GND
  FastLED.addLeds<WS2811, DATA_PIN, RGB>(leds, NUM_LEDS);
  black();
}

void loop() {
  manageStrip();
}

(typed here, fully untested)