brainstorm of brainfart to get some kind of global recognizable variable.

struct_for_globals.ino

#define NUMBER_OF_CHANNELS                  5
#define MAX_TIMERS                         50
#define MAX_NUMBER_OF_SENSORS               3

/**************************************************************************
       type definitions
**************************************************************************/
enum lightStatus_t
{
  LIGHTS_OFF, LIGHTS_ON, LIGHTS_AUTO
};

const char *lightStatusToString( const lightStatus_t status )
{
  switch ( status )
  {
    case LIGHTS_OFF:   return PSTR(" LIGHTS OFF");
    case LIGHTS_ON:    return PSTR(" LIGHTS ON ");
    case LIGHTS_AUTO:  return PSTR("LIGHTS AUTO");
    default:           return PSTR(" UNDEFINED ");
  }
}

struct lightTimer_t
{
  time_t      time;                    /* time in seconds since midnight so range is 0-86400 */
  uint8_t     percentage;              /* in percentage so range is 0-100 */
};

struct channelData_t
{
  lightTimer_t    timer[MAX_TIMERS];
  char            name[15];            /* initially set to 'channel 1' 'channel 2' etc. */
  char            color[8];            /* interface color, not light color! in hex format*/
  /*                                      Example: '#ff0000' for bright red */
  float           currentPercentage;   /* what percentage is this channel set to */
  uint8_t         pin;                 /* which ESP32 pin is this channel on */
  uint8_t         numberOfTimers;      /* actual number of timers for this channel */
  float           minimumLevel;        /* never dim this channel below this percentage */
};

struct sensorData_t                    /* struct to keep track of Dallas DS18B20 sensors */
{
  byte   addr[8];
  float  tempCelcius;
  char   name[15];
};

struct aquaControl_t
{
  private:
    lightStatus_t           _lightStatus                        = LIGHTS_OFF;
    channelData_t           _channel[NUMBER_OF_CHANNELS]        = {};
  public:
    const uint8_t           dimmerTaskPriority                  = 8;
  
    channelData_t           channel[NUMBER_OF_CHANNELS]         = {};
    sensorData_t            sensor[MAX_NUMBER_OF_SENSORS]       = {};
    lightStatus_t           lightStatus(){ return _lightStatus; };
    void                    setStatus( const lightStatus_t status )
    {
      portMUX_TYPE myMutex = portMUX_INITIALIZER_UNLOCKED;
      portENTER_CRITICAL(&myMutex); 
      _lightStatus = status; 
      portEXIT_CRITICAL(&myMutex);
    };
    lightTimer_t            timer( const uint8_t channel, const uint8_t number )
    {
      lightTimer_t value = { 3600, 67 }; /* seconds since midnight, percentage */
      return value;
    };
    bool                    insertTimer( const uint8_t channel, const uint8_t number, const float percentage )
    {
      //find position in timer list
      //insert timer
    };
};

aquaControl_t global;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  global.setStatus( LIGHTS_AUTO );
  Serial.println( lightStatusToString( global.lightStatus() ) );
  lightTimer_t aTimer = global.timer(13,4);
  Serial.println( aTimer.percentage );
}

void loop() {
  // put your main code here, to run repeatedly:

}