There isn't a direct way to link data validation to a checkbox value in Excel. However, you can achieve a similar outcome using a combination of a helper cell and a custom formula in data validation. Here's how:

1. Link Checkbox to Helper Cell:

- Place your checkbox somewhere on the sheet. Let's say it's in cell `A1`.
- In another cell, let's say `B1`, enter a formula to capture the checkbox value. You can use the `ISTEXT` function to check if the checkbox contains a value (TRUE translates to "text"). The formula in `B1` would be: `=ISTEXT(A1)`.

2. Conditional Data Validation based on Helper Cell:

- Select the cell(s) where you want to restrict data entry based on the checkbox.
- Go to the "Data" tab and click "Data Validation" in the "Data Tools" group.
- In the "Settings" tab, under "Allow," choose "Custom" from the dropdown menu.
- In the "Formula" box, enter a formula that references the helper cell (B1) and checks its value. Here's the breakdown:
- If the checkbox is checked (TRUE in B1), allow any data entry: `=B1=TRUE`
- If the checkbox is unchecked (FALSE in B1), restrict data entry (e.g., only allow text): `=AND(B1=FALSE,ISTEXT(A1))` - This formula ensures a value can only be entered if the checkbox is unchecked AND the entered value is text.

3. Additional Options:

- In the "Error Alert" tab, you can customize the error message that appears when someone tries to enter invalid data based on the checkbox state.
- You can adjust the data validation formula based on your specific needs. For example, you could allow only numbers when the checkbox is unchecked.

Explanation:

- The helper cell (`B1`) acts as a bridge between the checkbox and the data validation formula.
- The custom formula checks the value in the helper cell (`B1`) to determine the allowed data type.
- This approach allows you to dynamically control data entry based on the checkbox selection.

Note: This method requires an additional helper cell, but it provides a way to link data validation to the state of a checkbox in Excel.