I would like to receive notifications from Google Sheets when a checkbox is checked from a selected user ID. Please help me set this up!
How do you intend to send this notification ?
I'm new to programming, so I would like to receive notifications in my app when a checkbox is checked (TRUE) in Google Sheets.
Please help me with a simple way!
Just a single device, or all devices running your app ?
You could probably use this method:
and have an onEdit google apps script setup on the spreadsheet
Each user will install the app separately, and each user will have their own login.
For example, if user ID 1 is checked, then only user ID 1 name Dany should receive the notification
You will probably need one of the [PAID] notification extensions (OneSignal / Firebase Cloud Messaging) to achieve this.
I would like it for free! 
I would like to use Google Sheets as a database.
That is fine, but sending push notifications to individual users is a completely different ball game.
How will the checkbox be checked ?
When the checkbox is checked, it will be TRUE; otherwise, it will be FALSE.
By someone actually using the spreadsheet, or programatically using script/blocks...?
by someone using the spreadsheet
When the checkbox is checked, it will be TRUE; otherwise, it will be FALSE. If checked, a notification must be sent; otherwise, no notification is needed.
Yes, I get that
What is this checkbox signifying, what is the Status relating to ?
"It's just an example for starting to get a notification of the user's name when the status is Checked
Let us understand your workflow then.
What are you trying to achieve by checking a checkbox and sending a notification ?
You can simply make a (timed) call to the spreadsheet from your app to see if the cell is TRUE or FALSE