I hadn’t thought that Open in a New Tab would apply to a folder. It’s still a bit messy like that. And the problem is that it wouldn’t be persistent across launches.
I know another option would be to create aliases inside the iCloud folder, but that, too, can get messy. If you work on more than one Mac as I do, aliases don’t always work from one computer to another.
If it bothers you not only that each folder opens in its own window, but also that the iCloud folder is, so to speak, the main folder, then according to Matteo, that’s going to change.
But there’s really nothing more I can do to convince you that Lettera might be the right tool for you. 
I’ve gone over the discussion between @kirkmc and me again. Would it make sense to have an option so that when you select Main menu -> File -> Open… the folder opens in the currently active Lettera window instead of in a new window? It seems that some users don’t like having so many windows open and would rather stay in a single window as much as possible.
@kirkmc
Would that help you at all?
It would be an improvement over the current implementation, but I’m not sure how that works in practice. The fact that windows looking different according to how files are opened is problem from an overall interface perspective. Having the sidebar visible and active in some cases, and invisible and not even available in other cases is dissonant. One expects an app to behave consistently, and this is very inconsistent.
For me the app acts consistently. When I open a file from finder I expect nothing else than a window without sidebar. Look, even though it’s legitimate to have expectations of an app, it’s also okay to expect you to adapt to the app’s design.
But if I already have a window open with a sidebar, that’s where the cognitive dissonance arises.
It’s actually your cognitive dissonance. Let this be the starting point for changing your expectations. 
I’m thinking of any other app that has a sidebar; none of them disappear the sidebar when something happens. The sidebar has become a standard interface element, and when open, is expected to be open for all files. Apps like BBEdit and Xcode have persistent sidebars, not to mention all note taking apps, but they’re different since, in general, they aren’t managing individual files (even if something like Obsidian is, it doesn’t present them as files).
This said, most of these apps don’t default to a folder to store files. They assume you open files from anywhere, rather than store them by default in a dedicated iCloud folder. Perhaps that’s the real dissonance. This is a text editor that is leveraging a note-taking app, and perhaps trying to be too much like the note-taking app and not enough like a standalone text editor.
I say this as having reviewed dozens of text editors for Macworld Magazine during the 15 years I wrote for them, and still writing about text editors for another client.
So what? Lettera is a new app with its own approach. I am not able to see any better handling than opening a file from finder in its own window without sidebar.
Do you really think iA Writers way is more elegant?
Actually it is still your own dissonance. 
Are you saying that the iA Writer warning you circled there is a problem? I don’t see how, when you have two locations, an app alerting you to the fact that you’re editing a file that you might actually want to move to one of those locations is inelegant.
The difference with Lettera is that you can’t display the sidebar at all if you open an ad hoc file, whereas you might actually want to move the file to a location, either the iCloud folder or another one.
Of course I am. I opened the file just to see its content. Therefore it is a big distraction to see an ui of a whole workspace. I’m going to end this discussion on my end. I feel like someone who’s desperately trying to explain to another person who’s holding a screwdriver that he would be better off using a hammer if he wants to drive a nail into the wall.
Thats not what i meant. When i open a markdown file, either in the Finder or from the lettera file menu, id like the sidebar to be visible and showing the contents of the file’s containing folder.
Then why don’t you open this folder in Lettera? After all that’s exactly what the app is meant for. Lettera is meant to replace Finder. Plus, it also has a feature that lets you open a file from within Finder for viewing and editing. But then the context isn’t relevant anymore. I’m imagining opening a single markdown file in a folder that otherwise contains hardly any markdown files: the context displayed as a workspace would be distracting and unnecessary.
I explained why this is not always possible (sandbox permissions, etc.). So instead we decided to make the the app’s behavior predictable: the sidebar visible only when opening a folder, not when you open a file.
I think, the more I examine how I use text editors (including markdown editors) that support some form of workspace, the more I see I rely on being able to pull multiple folders with different roots into a single project.
I see less value in having to construct a project/workspace on my hard drive first and remember to save anything into that same workspace. Even Finder uses coloured tags to allow for sensible grouping of related items from different places on the hard drive. I see zero value in having to open multiple windows inside one app to achieve the same. That includes needing to have the sidebar displayed at all times if I don’t want to lose track of which folder is open inside each window—Lettera’s title bar currently won’t tell me anything about the file’s whereabouts.
For me, a true workspace-based app is composed of two main parts, the library (where the materials are gathered) and the work table (editor). This extends beyond just text editing (NLEs for example have the same philosophy), and a single-folder-as-workspace philosophy seems very limiting for no apparent benefit.
It doesn’t work for me. Never mind, there’s other choices, I’ll stick with what I have, thanks.
When I click to open the highlighted file, which lives on my Desktop, it opens as a second tab within the Lettera window.
The tab with the Greek charts is in my Lettera workspace, but the Preaching Questions file is not.
Thanks for the clarification as I initially agreed with OP as the behavior was different and as others assumed I too was expecting to see the sidebar of the parent folder of the file.
I thought well as a user if all I wanted to do was focus on this single file maybe I don’t need the noise from the sidebar, keeps it clean and focused. I was expecting to be able to toggle the sidebar on and off though.
This explanation helps add more reasoning behind it, thanks.
I’ve noticed that and have come to terms with it as combining folders simply complicates the coding and then you’re starting to recreate Finder. The whole point was the user manages their file structure outside of the app even though you do implement some file management within that one folder structure.
I found that using Window->Merge All Windows brings all the Folder windows together and when you select a Tab the corresponding folder shows up in the sidebar— win-win and no extra coding to make it work…it’s Apple’s window subsystem in action.
I expect the sidebar to remain as the file is displayed in the current tab or you can open it in its own tab.
