I can't keep a bash script alive in ubuntu 20.04

I found and slightly modify the following script, that monitor the notify-send notifications and dump them in a file.

#!/bin/bash

logfile=$1

dbus-monitor "interface='org.freedesktop.Notifications'" |\
 grep --line-buffered "string" |\
 grep --line-buffered -e method -e ":" -e '""' -e urgency -e notify -v |\
 grep --line-buffered '.*(?=string)|(?<=string).*' -oPi |\
 grep --line-buffered -v '^\s*$' |\
 ts |\
 xargs -I '{}' -d '\n' echo -e {} >> $logfile

If I run it manually:

notifylog notifylog.txt

the process keeps working for a while but eventually stops. If I add it to crontab like:

@reboot /path/to/file/notifylog /home/user/notifylog.txt

it executes once and then stops (or it last running very little).

I even tried adding it to the startup applications like:

/path/to/file/notifylog /home/user/notifylog.txt

and same result. The following works when executed manually but not from crontab or startup applications:

#!/bin/bash

logfile='/home/user/notifylog.txt'
rm -f $logfile
touch $logfile

while true; do /path/to/file/notifylog $logfile && break;done

I added to systemd with the following steps:

sudo nano /lib/systemd/system/notifylog.service

then I added:

[Unit]
Description=notify-send log

[Service]
ExecStart=/path/to/file/notifylog

[Install]
WantedBy=multi-user.target

then:

sudo systemctl daemon-reload
sudo systemctl enable notifylog.service
sudo systemctl start notifylog.service
sudo systemctl status notifylog.service

the last one gives me:

● notifylog.service - notify-send log
     Loaded: loaded (/lib/systemd/system/notifylog.service; enabled; vendor preset: enabled)
     Active: inactive (dead) since Wed 2021-10-20 19:01:49 -03; 3min 52s ago
    Process: 364180 ExecStart=/path/to/file/notifylog (code=exited, status=0/SUCC>
   Main PID: 364180 (code=exited, status=0/SUCCESS)

oct 20 19:01:49 mymachine systemd[1]: Started notify-send log.
oct 20 19:01:49 mymachine notifylog[364186]: Failed to open connection to session bus: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11
oct 20 19:01:49 mymachine systemd[1]: notifylog.service: Succeeded.

It doesn't seems to be running.

For this I modified the script a little:

#!/bin/bash

logfile='/home/user/notifylog.txt'
rm -f $logfile
touch $logfile

dbus-monitor "interface='org.freedesktop.Notifications'" |\
 grep --line-buffered "string" |\
 grep --line-buffered -e method -e ":" -e '""' -e urgency -e notify -v |\
 grep --line-buffered '.*(?=string)|(?<=string).*' -oPi |\
 grep --line-buffered -v '^\s*$' |\
 ts |\
 xargs -I '{}' -d '\n' echo -e {} >> $logfile

EDIT: now I added it to systemd as user with the following steps

First, add the .service file to /home/user/.config/systemd/user. Then execute:

sudo systemctl daemon-reload
systemctl --user enable notifylog.service
systemctl --user start notifylog.service
systemctl --user status notifylog.service

This start the service correctly, but if I reboot my machine,

systemctl --user status notifylog.service

gives me:

● notifylog.service - notify-send log
     Loaded: loaded (/home/user/.config/systemd/user/notifylog.service; enabled; vendor preset: enabled)
     Active: inactive (dead)

What I'm missing now?

What worked so far was changing the WantedBy section:

[Unit]
Description=notify-send log

[Service]
ExecStart=/path/to/file/notifylog
Restart=always

[Install]
WantedBy=default.target