First, create a sprite and set the size. Then fill it in black to avoid overwriting text.

disp_buffer = new TFT_eSprite(&M5.Lcd);
disp_buffer->setSwapBytes(false);
disp_buffer->createSprite(240, 135);
disp_buffer->fillRect(0, 0, 240, 135, BLACK);

Then write desired text and push it to screen.

disp_buffer->drawString("This is some text", 0, 0, 2);
disp_buffer->pushSprite(0, 0);

or try below commands in execute block
Print text on screen, x and y is beginning cursor , use current foreground color is not given
lcd.print(text, x, y, [,color])
Set the default foreground color
lcd.set_fg(color)

On 1.4.5 firmware looks like:
https://youtu.be/EzupP4tXkZA

Here is my attempt to reduce flicker for a simple counter. The code separates the digits and only updates the ones which are necessary. The flicker isn't completely gone, but at least only the digit which changes flickers a little bit.

from m5stack import *
from m5ui import *
from uiflow import *
import time

setScreenColor(0x000000)

count0 = None
oldten0 = None
one0 = None
ten0 = None

from numbers import Number
import math

count0 = 0
oldten0 = 0
for count in range(30):
  one0 = count0 % 10
  lcd.print(one0, 20, 5, 0x000000)
  count0 = (count0 if isinstance(count0, Number) else 0) + 1
  one0 = count0 % 10
  lcd.print(one0, 20, 5, 0xff0000)
  ten0 = math.floor(count0 / 10)
  if ten0 != oldten0:
    lcd.print(oldten0, 5, 5, 0x000000)
    lcd.print(ten0, 5, 5, 0xff0000)
    oldten0 = ten0
  wait_ms(300)

BTW: In the Arduino environment a solution to reduce flicker is to use sprites, but I have no idea if sprites exist in M5Stack's MicroPython implementation.

Cheers
Felix