Per today's Summer 21 release webinar, you will need to do two things

Add a new import:

import { CloseActionScreenEvent } from 'lightning/actions';

Then add a simple method to close it:

closeQuickAction() {
        this.dispatchEvent(new CloseActionScreenEvent());
    }

You can then call that and it will close the quick action

H/T to Fabien Taillon for the heads up on this one

Per today's Summer 21 release webinar, you will need to do two things

Add a new import:

import { CloseActionScreenEvent } from 'lightning/actions';

Then add a simple method to close it:

closeQuickAction() {
        this.dispatchEvent(new CloseActionScreenEvent());
    }

You can then call that and it will close the quick action. More details here

H/T to Fabien Taillon for the heads up on this one

Per today's Summer 21 release webinar, you will need to do two things

Add a new import:

import { CloseActionScreenEvent } from 'lightning/actions';

Then add a simple method to close it:

closeQuickAction() {
        this.dispatchEvent(new CloseActionScreenEvent());
    }

You can then call that and it will close the quick action

Per today's Summer 21 release webinar, you will need to do two things

Add a new import:

import { CloseActionScreenEvent } from 'lightning/actions';

Then add a simple method to close it:

closeQuickAction() {
        this.dispatchEvent(new CloseActionScreenEvent());
    }

You can then call that and it will close the quick action

H/T to Fabien Taillon for the heads up on this one