The Limitation
I want to redesign the mobile version of Slack and it will focus on the dark mode. The app that will be talked on this is version 20.09.10.0, updated on Sep 11, 2020 at Play Store.
Slack app has so many screens/pages. In this redesign, I will focus on the four main screens that can be accessed from the navigation bar at the bottom, plus when choosing the workspace and in the chat room (the private one).
The Plan
To do the redesign, we need to create some big steps:
`What’s the problem?
When I open the Slack app, the Home is showing the list of channels, direct message, the unreads, etc. For me, it’s like a people contact or settings with a lot of texts without visual. And for the chat, the tapping area is too small as the main screen.
Actually, Slack has ‘chat looks’ but it’s only for the direct message under the DMs menu. So, for me it’s a duplicate thing if in the home is the access to the unread chat, but we also have DMs.
For the Mentions menu, it’s actually not only the mentions. And for me it’s a waste to be a main navigation menu.
Another problem...
From the Home menu at first, we can swipe left and the app shows the list of our workspaces vertically with the menu for the active workspace on right. And also some menu on that, like People or Invite People could be in a proper screen in the workspace. The things that we need from that is preferences and sign out.
Next, for the Profile screen, it looks like... um.. yeah, a settings page.
And... actually I have a problem with Slack that has no information if our message is read or not.
`Solution!
First of all, we need to change the navigation menu at the bottom of the screen.
And here is my idea:

💬 Chat
Like the other messaging platform, it shows list of chat rooms, including the channel.
📗 Channel and People List
Like the contact feature, in this screen we can see all channel and people.
🔔 Notifications
Not only mentions, in this screen you can find if people react to your message, reply thread, etc. 
🙍‍♂️ Profile
Make it profile page looks-like. Need to change the layout for this.

And yes, we need to simplify the workspace selection screen, and update the chat room design.
`Wireframe, yeah!
Simple workspace selection screen. Wide tapping area for the chat room list, with the avatar (also default avatar for channels), and big floating button to start new conversation. Online/last seen indicator and information if our message is read in the chat room. Use the left-right layout to see which our messages easier and faster.
Have a ‘contact’ feature that includes all the channels and people. We also join/create the other channels here and invite a new member to the workspace. You can find the notification about someone reacted to your message, mentioned you in a channel, or if someone replied you on a thread. All notifications are in one place.
Last, it has a profile page like a profile page.
`High-Fidelity Time :D
Here are what I've done for the HiFi...
I'm using Montserrat as the typeface, the four colors from the Slack logo itself, and some black variant to create a good hierarchy. I tried to use the atomic design method by creating the smaller objects first like the chat room list below.
Thank You!

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Up, up, up!