Need to capture the value from a specific field on the standard record edit page in real-time, before the Save button is clicked on Salesforce

I need to capture the value from a specific field on the standard record edit page in real-time, before the Save button is clicked, validate it, and then display the corresponding alert in the custom LWC component.

I try to capture the value from the “Amount” field on the standard record edit page in real-time, validate it, and then display the appropriate alert in the custom LWC component.
Opportunity standard record edit page