Your comments

Understood. I would just set a variable in the prefs file to indicate whether an element should be visible or not at startup but that was all a long time ago and I no longer code software.

With 'Restore ..' checked, I have found that the app sometimes open with files that were not open when I closed it. On one occasion, it opened a single file which I had worked on but had closed before closing the app. On another occasion, it opened about a dozen files on which I had worked but had closed well before closing the app.

This happened regardless of if I had closed files by clicking the x on the tab or by using Command-w.

I still like the app but the number of stars is reducing.

Update:

As a workaround, I have created an empty, read-only file to keep the sidebar open without the app opening a real source file by default (which I would then have to close every time before starting work).

When I come to rate this program on the App Store, it is likely to get 4 stars as it stands - from which you may assume that I really like it a lot.

Precisely. That is the problem I was highlighting.

Perhaps those two unrelated settings could be dealt with separately - Restore files (for anyone who might need that) and Restore windows (for most users).

Every other program I have, including Safari from which I am sending this, remembers if a sidebar is visible. Safari does not also insist on opening my last webpage as well (unless I want it to).

I have tried both options. The sidebar only remains visible if I reopen a file.

I do not want files to reopen. I am unlikely to edit the same file repeatedly.

I want the sidebar to remain open and, ideally, for the folder placed there to remain in place at all times. From that folder on the sidebar, I can open and edit any source file I want. Why would the program want to behave in any other way?