For programming notes, the indent button on the mobile toolbar (can be added if it’s not there by default) adds tabs to the starts of lines by default. (Of course that doesn’t help if you’re trying to insert tabs later in the line to align comments or something, which I assume is what you’re doing.)
Another workaround is to make a template that contains only a tab. If triggering a template is too clunky, you can use a plugin to assign a command to it and add the command to the mobile toolbar.
That’s not how paragraphs work in Markdown. You use a blank line to mark them. If you want indented-style paragraphs you can use CSS change how they render, but the Markdown itself won’t be indented.