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.