How to add new line in Markdown presentation?

See the original markdown specification (bold mine):

The implication of the “one or more consecutive lines of text” rule is that Markdown supports “hard-wrapped” text paragraphs. This differs significantly from most other text-to-HTML formatters (including Movable Type’s “Convert Line Breaks” option) which translate every line break character in a paragraph into a <br /> tag.

When you do want to insert a <br /> break tag using Markdown, you end a line with two or more spaces, then type return.

How to add new line in Markdown presentation?

Check the following resource Line Return

To force a line return, place two empty spaces at the end of a line.

Just add \ at the end of line. For example

one\
two

Will become

one
two

It's also better than two spaces because it's visible.

Edit:
It doesn't work in some markdown applications, so it may cause incompatibility. https://www.markdownguide.org/basic-syntax/#line-break-best-practices