Starting Discussions

elementary uses GitHub to not only track issue reports but also for planning improvements and design changes.
If you want to start a larger conversation around a design change that could incorporate many smaller changes or needs some discussion before it can be actionable, you can use GitHub Discussions.
As described in Reporting Issues, you can use the Feedback app to find and open the relevant project page to start a new discussion or you can manually search for projects on GitHub. When you've found what looks like the right project, head over to the "Discussions" tab and select "Ideas" in the sidebar to see design proposals and conversations.
Just like when reporting issues, please search open discussions to see if you could be participating in an already open discussion before creating a new one.
To start a new discussion, select the green "New discussion" button in the top right and keep these tips in mind:

Reference GitHub Issues

A good design proposal should have clear design goals and often these can be expressed as GitHub issues. Referencing issues that should be considered and solved within the scope of this design discussion helps guide the direction of discussion and gives developers a way to start working towards solutions. Creating new issue reports as part of the design process can also have a few other benefits:
It will make your design proposal less intimidating. A big design proposal can mean a big time investment that will likely have to be taken on by someone volunteering their free time. Smaller changes that can be incorporated over time are more likely to be adopted and resolved
It allows developers to track their progress. Even if a developer wants to implement your entire proposal right away, they might not be able to. Giving them a way to “check off” pieces as they go makes it more likely that a part of your design won’t be forgotten about when it’s translated into code.
It allows developers to scope down your proposal. It's possible that some part of your proposal doesn't fit within the project scope or conflicts with another part of its design. Breaking up your overall proposal into smaller action items increases the change that at least some part of your proposal will be incorporated, even if other parts of it can't be.

Be Considerate

Designers are often opinionated and passionate people, but please try to remember that developers are people too. It's important to be objective about the current design of a project, but try to avoid disparaging others' work and keep in mind the Code of Conduct. The outcome of a design discussion should be exciting and inspiring and is an opportunity for collaborative problem solving.

Be Prepared to Iterate

If part of your proposal conflicts with an existing project goal or is considered out of scope, you might have to go back to the drawing board a bit! Developers may provide feedback that means your idea needs to change a little bit before it can be worked on. Designs can often go through many revisions or take some time before everyone is happy and work can begin.