You can put and trigger per this script every minute on google sheet appscript and get notification on slack channel.

slack-upwork-rss-feed-appscript-for-notification

function upworkJavaScript() {
  analyzeFeedAndSendSlack('A3', 
  "feed-url-on-upwork", 
  "slack-web-hook-url")
}

var getSheetById = (ss, sheetId) => {
  var foundSheets = ss.getSheets().filter(sheet => sheet.getSheetId() === sheetId);
  return foundSheets.length ? foundSheets[0] : undefined;
}
const sendAlert = (payload, webHookUrl) => {
  const webhook = webHookUrl;
  var options = {
    "method": "post",
    "contentType": "application/json",
    "payload": JSON.stringify(payload)
  };

  try {
    UrlFetchApp.fetch(webhook, options);
  } catch (e) {
    console.log(e)
    Logger.log(e);
  }
}

var analyzeFeedAndSendSlack = (cellValue, feedUrl, hookUrl) => {

  const ss = SpreadsheetApp.getActiveSpreadsheet()
  var sheet = getSheetById(ss, 0)
  const lastDate = sheet.getRange(cellValue).getValue()

  var txt = UrlFetchApp.fetch(feedUrl).getContentText();
  var document = XmlService.parse(txt);

  let root = document.getRootElement();

  let channel = root.getChild('channel');
  let items = channel.getChildren('item');
  let maxLastDate;
  console.log("lastDate -> " + lastDate)
  for (let i = items.length - 1; i >= 0; i--) {
    let pubDate = new Date(items[i].getChild('pubDate').getValue())
    //console.log("pubDate : " + pubDate + " guid :" + items[i].getChild('guid').getText())
    //console.log("decc : " + decc + "- punDate : " + pubDate + " condition : ")
    //console.log("pub date naked: " + pubDate + " guid :" + items[i].getChild('guid').getText())
    if (lastDate < pubDate) {
      //console.log("pubDate : " + pubDate + " guid :" + items[i].getChild('guid').getText())
      let desc = new String(items[i].getChild('description').getText())
      desc = desc.replaceAll("<br />", "\n").replaceAll("<b>", "*").replaceAll("</b>", "*")
      let payload = {
        "text": items[i].getChild('title').getText(),
        "blocks": [
          {
            "type": "header",
            "text": {
              "type": "plain_text",
              "text": items[i].getChild('title').getText(),
              "emoji": true
            }
          },
          {
            "type": "section",
            "block_id": "section565",
            "text": {
              "type": "mrkdwn",
              "text": "<" + items[i].getChild('link').getText() + "|job link> \n "
            }
          },
          {
            "type": "section",
            "block_id": "section567",
            "text": {
              "type": "mrkdwn",
              "text": desc
            }
          }
        ]
      }
      console.log("sent : " + items[i].getChild('guid').getText())
      sendAlert(payload, hookUrl)
      //sent slack
      if (maxLastDate != null && maxLastDate != "") {
        //console.log("if maxLastDate -> " + maxLastDate)
        maxLastDate = pubDate > maxLastDate ? pubDate : maxLastDate
      } else {
        //console.log("if else  pubDate -> " + pubDate)
        maxLastDate = pubDate
      }
      console.log("last maxLastDate -> " + maxLastDate)
    } else {
      //console.log("no record found")
    }
  }
  if (maxLastDate != null && maxLastDate != "") {
    console.log("convertToDateTurkeyTimeZone(maxLastDate) -> " + maxLastDate)
    sheet.getRange(cellValue).setValue(maxLastDate);
  }
}