Disabling Steam Chat's automatic popup at Windows login startup

Recently as of this writing (27 July 2018), Steam has begun opening the chat Friends popup whenever I login to my Windows 10 account:

I can't figure out how to stop this without disabling Steam itself from starting up—which I want it to do, for auto-updating and so that my VR headset will be ready.

On Steam Communities, there's a prevalent suggestion that the following sequence can stop this:

1. After logging in and the Steam chat window opens, open the full Steam app.
2. Close the Steam chat window.
3. Close Steam's app window.
4. Relog from Windows.

but in my trials, this has no effect.

There are no obvious settings for this by clicking the gear icon (highlighted in red in the above image):

I found what seemed to be a promising option in the Steam application's settings → "Interface" → "Set Taskbar Preferences":

but, as advertised, it only affects the choices available if you right-click on the Steam icon in the taskbar:

Unticking "Friends" and relogging does not change the popup behavior at startup.

How can I prevent this window from opening every time I login? The Steam application itself opens in the background; I'd like the chat to do the same.

Solution 1:

This is fixed in the latest beta, and should be a part of the next public client update. announcement:

Friends & Chat - Beta Client Only

• Added 'Do Not Disturb' mode. When selected, the user will receive no notifications from friends or groups, incoming chat messages will not open new chat windows or play an incoming message sound.
• Added 'Offline' as a selectable status. This will log the user's client out of Steam Friends and the user will appear as offline to their friends.
• Added the option to not automatically log into Steam Friends at Steam Client startup.
• Fix for inadvertently opening the friends list at client start even though it was previously closed when Steam was shutdown. Please report any further instances of this bug in Steam Client Beta Discussions.

Friends & Chat - All Users

• EXIF data within JPG images is now stripped on upload.
• Clicking your avatar at the top of the friends list now takes you to your profile.
• Fixed not being able to close the friends list or chat windows when in a disconnected state.
• Added /quote for formatting text as a block quote.
• Friends will now have a special indicator when displayed in a group member list
• More compact chat entry space and chat tabs when Compact View is selected. Fixed a bug where extra space was being added to chat lines when only one line was sent.
• Embedded videos and images start a little smaller, you can still scale them up by dragging.

In a way it's nice that they're mostly using pure HTML/CSS/JS for the new chat as it's very easy for them to add new features in comparison to the old client, but they really should've put more work into porting existing features & UI settings.