[main.cpp]
#include <PVinverter.h>
// inverter lib constructor
PV_INVERTER inverter(Serial2);

#include <PVinverterLCD.h>
//U8G2_ST7920_128X64_F_SW_SPI u8g2(U8G2_R0, /* clock=*/ 25, /* data= /R/w */ 33, /* CS=*/ 32, /* reset= */ U8X8_PIN_NONE );  // ESP32
PVinverterLCD lcd( 25, 33,32, U8X8_PIN_NONE);

[....]
[pvinverter.h]

class PV_INVERTER
{
   public:
[...]
 typedef struct DevStatus_t
    {
      bool changingFloatMode = 0 ;
      bool SwitchOn = 0 ;
      bool dustProof = 0 ;
      bool SBUpriority = 0 ;
      bool ConfigStatus = 0 ;
      bool FwUpdate = 0 ;
      bool LoadStatus = 0 ;
      bool BattVoltSteady = 0 ;
      bool Chargingstatus = 0 ;
      bool SCCcharge = 0 ;
      bool ACcharge = 0 ;
    } DevStatus_t;

devStatus_t DevStatus;


[...]
[PVinverterlcd.h]
#ifndef INVERTERLCD_H
#define INVERTERLCD_H

  #ifndef ARDUINO_H
    #include <Arduino.h>
  #endif

  #include <PVinverter.h>
  #include <U8g2lib.h>

  #ifdef U8X8_HAVE_HW_SPI
    #include <SPI.h>
  #endif

class PVinverterLCD
      {
[...]
[PVinverterLCD.CPP]

extern struct DevStatus_t DevStatus;

void PVinverterLCD::QPIGS()
{
 [...]
  u8g2.setFont(_INVLCD_DISP_font);
  bool a = DevStatus.ACcharge;                             // error: invalid use of incomplete type 'struct DevStatus_t'
  u8g2.drawStr(0,10,(const char*)a);
  u8g2.sendBuffer
}