The first impressions of an app are critical. This is the screenshot that I have when I have first installed the Matermost desktop client on Ubuntu. I think it will be the same for all platforms:

https://imgur.com/a/HY7FxOv

Almost everything on this screen is unfriendly to a new user especially a non-technical user.

1. The title

It just says: 'Add Server'. Nothing like 'Hi!' or 'Welcome to Mattermost!' or anything that displays some kind of enthusiasm for welcoming the user. This is where Slack shines - friendly, quirky (perhaps later annoying) messages.

2. Server Display Name

Even as a fairly technical user (CS university degree, 20 years web development experience, installed 4-5 different Linux distributions, 17k reputation across Stack Exchange) I have no clue as to what this means.

Questions that I have as a dumb user (note that this screen makes me feel like a dumb user - which is really bad):

1. Is this optional?
2. Where can I find the server name?
3. Can I choose my own?

The help text is: 'The name of the server displayed on your desktop app tab bar.'. But I don't have anything displayed there. What is my 'desktop app tab bar'? I don't know what that is.

The placeholder text 'Server Name' doesn't help at all

3. My suggestion

This my guess at what I think you could display. This would only need to be displayed for the first server it could be simplified for later servers, once a user has added one server then they will have a mental model of what will happen, but until then the extra friendly explanation really helps.

Title: Welcome to Mattermost! Let's connect your first server

Label: Your server address (URL)
Placeholder: https://example.com
Help text: The URL of your Mattermost server. It needs to start with http:// or https://.

Label: [optional] Give your server a display name
Placeholder: Choose any characters or emojis - go wild
Help text: This will be displayed in your side bar once you've added it

If you need more help here's our [getting started guide](...)