Supposed to according to whom? AP style, which is the standard for most English non-academic content, says one space. https://x.com/APStylebook/status/1254786139539427329

(Sorry for using Twitter as a source, but it's straight from AP)

I don't know why I love the sassiness in this reply. I'm 42 and I do it too.

It is not literally how you're supposed to write. It's an optional convention that has been increasingly falling out of favor over the decades.

Sentence Spacing (Wikipedia)

The desired or correct sentence spacing is often debated, but most sources now state that an additional space is not necessary or desirable. From around 1950, single sentence spacing became standard in books, magazines, and newspapers, and the majority of style guides that use a Latin-derived alphabet as a language base now prescribe or recommend the use of a single space after the concluding punctuation of a sentence. However, some sources still state that additional spacing is correct or acceptable. Some people preferred double sentence spacing because that was how they were taught to type. The few direct studies conducted since 2002 have produced inconclusive results as to which convention is more readable.

It is, and the confusion surely stems from the internet wherein HTML renderers (all web browsers) automatically collapse multiple spaces into one. Don't believe me? Every sentence in this post has two spaces in between.

This is literally how you're supposed to write.

How do you hand write a double space?

bark on em 👺