The issue turned out to be a faulty SD card.

I had tried other SD cards but must have used incorrect wiring for them.

The issue turned out to be a faulty SD card.

I had tried other SD cards but must have used incorrect wiring for them.

EDIT: Here is the updated code:

#define CS        5
#define SCK       18
#define MOSI      23
#define MISO      19

SPIClass spi(VSPI);

int setup_sd_card() {
  spi.begin(SCK, MISO, MOSI, CS);

  if (!SD.begin(CS,spi,4000000)) {
    Serial.println("ERROR: SD Card Mount Failed");
    delay(1000);
    return -1;
  }
  Serial.println("Finished initializing SD card. Getting card type...");

  uint8_t cardType = SD.cardType();
  
  if(cardType == CARD_NONE){
    Serial.println("ERROR: No SD card attached");
    delay(1000);
    return -1;
  }

  Serial.print("SD Card Type: ");
  if (cardType == CARD_MMC){
    Serial.println("MMC");
  } else if(cardType == CARD_SD){
    Serial.println("SDSC");
  } else if(cardType == CARD_SDHC){
    Serial.println("SDHC");
  } else {
    Serial.println("UNKNOWN");
  }
  Serial.printf("Total space: %lluMB\n", SD.totalBytes() / (1024 * 1024));
  Serial.printf("Used space: %lluMB\n", SD.usedBytes() / (1024 * 1024));

  Serial.println("SUCCESS! (SD CARD)");
  
  return 1;
}