Address all Desktop UI app review comments (post-migration)

To ensure isolation testing remains a simple task, the desktop UI was migrated to a separate app as-is, where possible.

- #5912

Some of the duplicated code has been identified as outdated or requiring improvement. These should _all_ be addressed. However, doing this all at once would lead to complexity in isolating any issues.

This issue is to track the completion of all review comments.

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