Why is my engine signal on?

You should check this with an OBD scanner, as 2018-2024 VW Tiguans have had significant engine issues. There’s a class action lawsuit against VW in the USA and Canada over this. If you’re noticing low oil levels or oil leaks, the most common culprit is a faulty PCV valve, so it’s worth getting it inspected.

As @kashifkhan71851 stated, the car's engine computer is telling you that it's seeing a fault related to the engine. It could be minor or it could be major; there's no way to tell without reading the Diagnostic Trouble Code(s) stored in the computer's memory. An OBD-II scanner is required to read those; such scanners can be obtained for anywhere from under $5 USD to several thousand dollars. Here in the US, most auto parts stores will scan your car for free and give you a list of the code or codes that are present.

Most scanners have the capability to turn off the "check engine", or Malfunction Indicator Light, but of course if the problem hasn't been fixed, it'll just come back on again, so you have to actually fix whatever is wrong before you get the engine codes cleared.

Assuming you get a list of the code or codes, come on back and add that information to your question, along with the year, engine size, transmission type and any submodel information about your car that's relevant. Once we have that, we should be able to help you figure out what's wrong and how to fix it.