How can we make a text field editable when the checkbox field on the same record is checked??

@Rohit Arora (N/A) 

To achieve in using validation rules:

 Set the criteria to fire when the checkbox is unchecked (FALSE) and the text field is changed. The formula might look like this: 

AND(
    NOT(Checkbox_Field__c),
    ISCHANGED(Text_Field__c)
)

Using Lightning Web Components

handleChange(event) {
    // This correctly captures whether the checkbox is checked or not.
    this.isTextFieldEditable = event.target.checked;
}

exampel:

<lightning-input type="checkbox" label="Enable Editing" onchange={handleChange}></lightning-input>
<!-- Use the `not` operator (!) to inverse the boolean value for the `disabled` attribute -->
<lightning-input type="text" label="Editable Text Field" disabled={!(isTextFieldEditable)}></lightning-input>

check below article:

• https://salesforce.stackexchange.com/questions/53752/how-to-make-a-field-editable-only-if-a-checkbox-is-checked