Fluent messaging app concept

Here's my concept desktop messaging app. It's the first time I've taken on designing any app, so I realize there are mistakes in here that I'm simply not aware of.

Since this is all quite new to me, the use of the words "fluent design" is very loose. I was merely inspired by this look, definitely wasn't attempting to adhere to any strict guidelines.

Everything was made in Figma.

If you have any feedback, don't hesitate to share your thoughts. I'm happy to learn.