It seems that FastLED.h lack of some developper to get it working properly on ESP32 now.
I jumped to AdaFruit NeoPixel lib and run this sketch successfully using your PIN values.
#include <M5Core2.h>
#include <Adafruit_NeoPixel.h>
#define LEDBAR_PXL 10
#define LEDBAR_PIN 25
Adafruit_NeoPixel ledBar(LEDBAR_PXL, LEDBAR_PIN, NEO_GRB + NEO_KHZ800);
void setup() {
M5.begin();
// put your setup code here, to run once:
ledBar.begin();
ledBar.show();
}
void loop() {
// put your main code here, to run repeatedly:
ledBar.fill(0xFF0000);
ledBar.show();
delay(750);
ledBar.fill(0x000000);
ledBar.show();
delay(500);
}