I am searching for an Markdown Editor, with a similar Live-Preview feature to Obsidian. In particular, I do not want to split the view into source and preview, but have the preview as the main window and only switch to source code for the line/block I am currently editing.
Nextcloud uses a similar feature for their in-browser editor, but I need an offline variant.
Joplin has this functionality, although I don’t often use it since I prefer to type directly into the Markdown editor. Whatever you choose, be sure that you’re comfortable with the security and privacy implications of it.
I use zettlr -- it's pretty good! The only issues I've run into are with the table editor, and with occasional lag on large documents; the latter just comes with the territory on an Electron app. I know Nathan's working on both, though.
QOwnNotes (https://github.com/pbek/QOwnNotes) may be an option as it is pure Markdown and need not have both the code and preview windows open. I used it before moving to Obsidian. It has some options to customise its window views, but it is a long time since I used it, so not sure if it has that block mode you want. Logseq I seem to recall worked with blocks as it is an Outliner that does save in Markdown format, but I did not like that the outline blocks added characters to the file format that slightly broke compatibility with standard Markdown formats. But blocks was Logseq's strength.
https://github.com/TriliumNext/Notes is a fork that appears to be actively developed. Found it near the end of the issue linked from the maintenance notice.