calling `log stream --predicate` command via `subprocess` does not append logs to stdout

Question

I’m writing a python script which calls the below commmand via subprocess and stores the logs to output.txt for further parsing

log stream --level debug --predicate 'subsystem contains "com.apple.UVCExtension" and composedMessage contains "Post PowerLog"'

when I execute this command in the terminal, the logs stream produces output like below

Filtering the log data using "subsystem CONTAINS "com.apple.UVCExtension" AND composedMessage CONTAINS "Post PowerLog""

Timestamp                       Thread     Type        Activity             PID    TTL
2022-02-17 17:07:51.336951+0530 0xbb0f0    Default     0x0                  369    0    UVCAssistant: (UVCExtension) [com.apple.UVCExtension:device] UVCExtensionAppleDevice:0x1000005fe [0x7f8sffea0he80] Post PowerLog {
    "VDCAssistant_Device_GUID" = "XXXXX";
    "VDCAssistant_Power_State" = On;
}
2022-02-17 17:07:52.241387+0530 0xbb0f0    Default     0x0                  369    0    UVCAssistant: (UVCExtension) [com.apple.UVCExtension:device] UVCExtensionAppleDevice:0x1000004ty [sdg4566679e80] Post PowerLog {
    "VDCAssistant_Device_GUID" = "XXXX";
    "VDCAssistant_Power_State" = Off;
}

However while calling the same command via subprocess, I'm unable to see any of the log values. I just see the first line of output. I want to parse the "ON" "Off" status of VDCassistant.

This is my python code

import subprocess
from threading import Thread
from time import sleep


def func1():
    f = open("output.txt", "w")
    subprocess.call(['log', 'stream','--style', 'json' , '--predicate', '(subsystem contains "com.ale.UVCExtension") and (composedMessage contains "Post PowerLog")'], stdout=f, stderr=f)
    return f

def func2():
    while True:
        sleep(5)
        with open("output.txt", "r") as file:
            result = (list(file))
            print(result)
            if "On;" in result:
                print (On status)
            else:
                print ("Off status")

if __name__ == '__main__':
    Thread(target = func1).start()
    Thread(target = func2).start()

What is going wrong here?