How to Disable PWAs in Microsoft Edge/Chrome browser

How to prevent Progressive Web Apps (PWAs) from installing on your desktop. 

A PWA is a web-based app created using HTML, CSS, and JavaScript that can be installed from a website like a regular desktop application. Once installed, the operating system will create a PWA shortcut and add it to Add or Remove Programs in Windows and under the /Users/<account>/Applications/ folder in macOS.

Recently these have been used to steal credentials and are unsafe. 
New phishing toolkit uses PWAs to steal login credentials (bleepingcomputer.com)

In Edge, type in address bar about://flags, search for 'handling' and change the settings to match image below. All settings that required changes are now all changed to Disabled. 

about://flags, search for 'PWA'

and change the settings to match image below.  All settings that are required to change are now all changed to Disabled. 

about://settings, search for 'application'

Change to off position as in image below.

about://settings, search for 'protocol'

Change to off position as in image below.

about://settings, search for 'apps'

Turn on Block Potentially Unwanted Apps.

Microsoft Defender SmartScreen must be enabled to turn on Block Potentially Unwanted Apps.
But note MDSS, talks to Microsoft servers, and is a privacy leak. 

Service workers are used by PWAs. To list and delete current service workers type in address bar

chrome://inspect/#service-workers

To disable you need an add-on unfortunately.

How to disable Service Workers on Chromium based browsers through uBlock · bonina.eu

Sources: 

PWAs as URL Handlers  |  Capabilities  |  Chrome for Developers

Handle protocols in Progressive Web Apps - Microsoft Edge Developer documentation | Microsoft Learn