How to create a CDK trigger using an existing lambda function

Question

I want a CDK after-deployment trigger. Triggers seem to be limited to lambda functions. I have an existing lambda function I'd like to use. I'm using typescript.

The triggers constructor which expects TriggerProps which expects a Function instead of something matching IFunction. This seems like a flaw/bug in the code?

My desired code is this:

const existingLambda = lambda.Function.fromFunctionArn(
  this,
  "myExistingLambdaID",
  "arn:aws:lambda:us-xxx-1:##########:function:myFunctionName"
);


const ciTrigger = new triggers.Trigger(this, 'MyTrigger', {
  handler: existingLambda,
});

However, this rejects with

Type 'IFunction' is missing the following properties from type 'Function': currentVersion, runtime, canCreatePermissions, _layers, and 37 more.ts(2740)

Is there another CDK native way to achieve this? (i don't want to do this in bash, etc)