diff --git a/Marlin/src/HAL/HAL_SAMD51/HAL.cpp b/Marlin/src/HAL/HAL_SAMD51/HAL.cpp
index 2b8da883dc..4828c40ff7 100644
--- a/Marlin/src/HAL/HAL_SAMD51/HAL.cpp
+++ b/Marlin/src/HAL/HAL_SAMD51/HAL.cpp
@@ -427,7 +427,6 @@ void HAL_init() {
     dma_init();
   #endif
   #if ENABLED(SDSUPPORT)
-    // SD_DETECT_PIN may be removed if NO_SD_HOST_DRIVE is not defined in Configuration_adv.h
     #if SD_CONNECTION_IS(ONBOARD) && PIN_EXISTS(SD_DETECT)
       SET_INPUT_PULLUP(SD_DETECT_PIN);
     #endif
@@ -496,14 +495,14 @@ void HAL_adc_init() {
       // Preloaded data (fixed for all ADC instances hence not loaded by DMA)
       adc->REFCTRL.bit.REFSEL = ADC_REFCTRL_REFSEL_AREFA_Val;               // VRefA pin
       SYNC(adc->SYNCBUSY.bit.REFCTRL);
-      adc->CTRLB.bit.RESSEL = ADC_CTRLB_RESSEL_12BIT_Val;
+      adc->CTRLB.bit.RESSEL = ADC_CTRLB_RESSEL_10BIT_Val;                   // ... ADC_CTRLB_RESSEL_16BIT_Val
       SYNC(adc->SYNCBUSY.bit.CTRLB);
       adc->SAMPCTRL.bit.SAMPLEN = (6 - 1);                                  // Sampling clocks
-      adc->AVGCTRL.reg = ADC_AVGCTRL_SAMPLENUM_16 | ADC_AVGCTRL_ADJRES(4);  // 16 Accumulated conversions and shift 4 to get oversampled 12 bits result
-      SYNC(adc->SYNCBUSY.bit.AVGCTRL);
+      //adc->AVGCTRL.reg = ADC_AVGCTRL_SAMPLENUM_16 | ADC_AVGCTRL_ADJRES(4);  // 16 Accumulated conversions and shift 4 to get oversampled 12 bits result
+      //SYNC(adc->SYNCBUSY.bit.AVGCTRL);
+
       // Registers loaded by DMA
       adc->DSEQCTRL.bit.INPUTCTRL = true;
-
       adc->DSEQCTRL.bit.AUTOSTART = true;                                   // Start conversion after DMA sequence
 
       adc->CTRLA.bit.ENABLE = true;                                         // Enable ADC
diff --git a/Marlin/src/HAL/HAL_SAMD51/HAL.h b/Marlin/src/HAL/HAL_SAMD51/HAL.h
index 2eaa40f302..209514a704 100644
--- a/Marlin/src/HAL/HAL_SAMD51/HAL.h
+++ b/Marlin/src/HAL/HAL_SAMD51/HAL.h
@@ -122,14 +122,14 @@ uint8_t eeprom_read_byte(uint8_t *pos);
 //
 // ADC
 //
-extern uint16_t HAL_adc_result;     // result of last ADC conversion
+extern uint16_t HAL_adc_result;     // Most recent ADC conversion
 
 #define HAL_ANALOG_SELECT(pin)
 
 void HAL_adc_init();
 
-#define HAL_ADC_FILTERED            // Disable oversampling done in Marlin as ADC values already filtered in HAL
-#define HAL_ADC_RESOLUTION  12
+//#define HAL_ADC_FILTERED          // Disable Marlin's oversampling. The HAL filters ADC values.
+#define HAL_ADC_RESOLUTION  10      // ... 12
 #define HAL_START_ADC(pin)  HAL_adc_start_conversion(pin)
 #define HAL_READ_ADC()      HAL_adc_result
 #define HAL_ADC_READY()     true
diff --git a/Marlin/src/HAL/HAL_SAMD51/HAL_SPI.cpp b/Marlin/src/HAL/HAL_SAMD51/HAL_SPI.cpp
index 4fe4c85b69..83226daa48 100644
--- a/Marlin/src/HAL/HAL_SAMD51/HAL_SPI.cpp
+++ b/Marlin/src/HAL/HAL_SAMD51/HAL_SPI.cpp
@@ -46,9 +46,6 @@
   // ------------------------
   #error "Software SPI not supported for SAMD51. Use Hardware SPI."
 
-  #if SD_CONNECTION_IS(ONBOARD)
-  #endif
-
 #else // !SOFTWARE_SPI
 
   #ifdef ADAFRUIT_GRAND_CENTRAL_M4
diff --git a/Marlin/src/HAL/HAL_SAMD51/fastio.h b/Marlin/src/HAL/HAL_SAMD51/fastio.h
index b5045e47bb..c91965e19e 100644
--- a/Marlin/src/HAL/HAL_SAMD51/fastio.h
+++ b/Marlin/src/HAL/HAL_SAMD51/fastio.h
@@ -245,6 +245,7 @@
   #define DIO17_PIN   PIN_PC23
   #define DIO88_PIN   PIN_PC24    // NEOPIXEL
   // PORTD
+  #define DIO53_PIN   PIN_PD10
   #define DIO22_PIN   PIN_PD12
   #define DIO6_PIN    PIN_PD20
   #define DIO7_PIN    PIN_PD21
diff --git a/Marlin/src/HAL/HAL_SAMD51/pinsDebug.h b/Marlin/src/HAL/HAL_SAMD51/pinsDebug.h
index 07964fb1b3..15b6473382 100644
--- a/Marlin/src/HAL/HAL_SAMD51/pinsDebug.h
+++ b/Marlin/src/HAL/HAL_SAMD51/pinsDebug.h
@@ -149,5 +149,6 @@ void pwm_details(int32_t pin) {
  *  92             |  PA9   | QSPI: IO1
  *  93             |  PA10  | QSPI: IO2
  *  94             |  PA11  | QSPI: IO3
+ *  95             |  PB31  | SD: DETECT
  *
  */
diff --git a/Marlin/src/inc/Conditionals_post.h b/Marlin/src/inc/Conditionals_post.h
index ef7df41a1c..624de26a0b 100644
--- a/Marlin/src/inc/Conditionals_post.h
+++ b/Marlin/src/inc/Conditionals_post.h
@@ -300,7 +300,7 @@
 /**
  * Override here because this is set in Configuration_adv.h
  */
-#if HAS_LCD_MENU && DISABLED(ELB_FULL_GRAPHIC_CONTROLLER)
+#if HAS_LCD_MENU && DISABLED(ELB_FULL_GRAPHIC_CONTROLLER) && !(defined(ARDUINO_GRAND_CENTRAL_M4) && SD_CONNECTION_IS(ONBOARD))
   #undef SD_DETECT_INVERTED
 #endif
 
@@ -2218,7 +2218,7 @@
 #endif
 
 #if ENABLED(SDSUPPORT)
-  #if SD_CONNECTION_IS(ONBOARD) && DISABLED(NO_SD_HOST_DRIVE)
+  #if SD_CONNECTION_IS(ONBOARD) && DISABLED(NO_SD_HOST_DRIVE) && !defined(ARDUINO_GRAND_CENTRAL_M4)
     //
     // The external SD card is not used. Hardware SPI is used to access the card.
     // When sharing the SD card with a PC we want the menu options to