Conditional formatting if a cell matches one from a list of a different sheet using Apps Script

Solution 1:

You can create an installable onEdit() trigger for your Potential Cities Spreadsheet which checks the Blocked Zips sheet for a match and applies some kind of formatting accordingly.

For example:

function checkForBlockedZips(e) {
  // do nothing if not column D
  if (e.range.getColumn() !== 4) return

  // get list of zips from blocked zips sheet
  const blockedZipsSsId = "your-spreadsheet-id"
  const blockedZipsSs = SpreadsheetApp.openById(blockedZipsSsId)

  const blockedZipsSheet = blockedZipsSs.getSheetByName("Sheet1")
  const zipCodes = blockedZipsSheet.getRange("A2:A").getValues()
    .flat(2)
    .filter(x => x)

  // check if the entered value is in the list of blocked zips
  if (~zipCodes.indexOf(e.range.getValue())) {
    // create cell style
    const strikethrough = SpreadsheetApp.newTextStyle()
      .setStrikethrough(true)
      .build()
  
    const richText = SpreadsheetApp.newRichTextValue()
      .setText(e.range.getValue())
      .setTextStyle(strikethrough)
      .build()
    
    // set the cell to have the desired rich text style
    e.range.setRichTextValue(richText).setBackground("yellow")
  }
  else {
    // if the value is not a blocked zip then reset the cell style 
    const nostrikethrough = SpreadsheetApp.newTextStyle()
      .setStrikethrough(false)
      .build()

    const richText = SpreadsheetApp.newRichTextValue()
      .setText(e.range.getValue())
      .setTextStyle(nostrikethrough)
      .build()

    e.range.setRichTextValue(richText).setBackground("white")
  }
}

Things to note:

• You need to use e.range.getValue() instead of e.value so that copy/pasted values can be read
• You need to add this script to the Potential cities sheet and authorise it as an installable trigger