This is very nice.
I suggest adding a preference setting to define the extension for the log files.
The case is: use this macro as a logger to post to a folder in an Obsidian vault (folder in iCloud). I personally have no use for .txt files. I think other users of markdown for capture log notes would have use for that option.
I modified the macro to change .txt to .md wherever needed to satisfy the logic. Works nice as a front end logger for Obsidian from anywhere.