I searched for a long time on a allot of sites including this one. I found again A LOT of death end topics.
and no answers so finaly I registerd here to asked for help.
HELP

in the below code is on of the manny things I tried without any result.
On my scope hoewever showed me Hello afther a uart.write("Hello") so the UART works
The pins are just for some program status leds en the while loop so I had some time to check the wiring.
just a line of code to write to the nextion display so I'm on my way...
Tnx
from pyb import UART
from pyb import Pin
import time
p_start = Pin('Y12', Pin.OUT_PP)
p_stop = Pin('Y11', Pin.OUT_PP)
p_start.high()
teller = 1
uart = UART(3, 9600)
#uart.init(9600, bits=8, parity=None, stop=1)
while teller < 1000:
uart.write('t1.txt="Hello"')
uart.write('\xFF\xFF\xFF')
p_stop.high()
time.sleep_ms(500)
p_stop.low()
time.sleep_ms(500)
teller = teller + 7
p_stop.high()
time.sleep(2)
p_start.low()
p_stop.low()