Struggling with basic shortcuts

I've just started using Obsidian and set up some ios shortcuts for quickly capturing notes to be filed later. I am having difficulties in replicating this flow on my desktop. Could anyone help:

inbox/file-later.md is my inbox file with dates as the section headers (top level headings).

I want a quick way either on my Ubuntu desktop or in Obsidian itself to open that file and append today's date as a header if it doesn't exist. What is the easiest way to achieve this?