Outlook "Hello World" sample Add-In doesn't respond on web browser, only in desktop client (MacOS)

Question

Hi,

I've been trying to get a development add-in to work in Outlook. It works just fine in the desktop client, but is non-functional in the browser version of outlook. (Google Chrome Version 118.0.5993.117, macOS Sonoma 14.5)

The add-in in question is the Hello World for Outlook sample add-in hosted here: https://github.com/OfficeDev/Office-Add-in-samples/blob/main/Samples/hello-world/outlook-hello-world

This add-in is supposed to bring up an "add-in task pane" whenever clicked whilst viewing a draft.

I downloaded the files in the folder linked above.

I then followed the instructions on https://learn.microsoft.com/en-gb/office/dev/add-ins/outlook/sideload-outlook-add-ins-for-testing to manually sideload the add-in. I selected the manifest.xml file in the add-in folder and accepted the dialogs that appear. I am not running a webserver on my machine. manifest.xml sources its files from the Github repository.

I then went to compose a message. I clicked the Add-Ins icon which brings up the window showing two add-ins. The "Hello World for Outlook" add-in appears to have been successfully installed, as in the image below.

Clicking the add-in does nothing on the browser. No error appears in console or anywhere else.

I tried to use the add-in in the desktop client. Clicking the app brings up the side task pane as expected: