Is Pride and Prejudice by Jane Austen written in Old, Middle, or Modern English?

I think there's a tendency to underestimate just how radically different Old English, Middle English, and Modern English are from one another, and the degree to which the English language has evolved across the centuries. Consider how often Shakespeare is referred to as Old English. In truth, Shakespeare is Modern English. He's antiquated Modern English, but he's Modern English nonetheless. Old English refers to the language as it existed from around 450 CE to around 1150 CE (see attached web-link from the British Library). This isn't merely antiquated: this is a language that modern English speakers would not be able to understand without specialized training. To see what Old English looks like, I'd refer you to the original untranslated Beowulf, which begins as follows: "Hwaet. We Gardena in geardagum,/beodcyninga, brym gefrunon..." That is an example of Old English. Middle English, on the other hand, is used in reference to the time frame which lasts until around roughly 1500 CE (an example of Middle English can be found in Chaucer). Thus, Jane Austen, who lived from 1775 to 1817, is very much an example of Modern English (which is reflected in the language which she used). Take Pride and Prejudice, which begins as follows: "It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of a wife." This language is far more contemporary than the sort of language one might find in Chaucer, let alone in Beowulf.
https://www.bl.uk/medieval-literature/articles/old-english

Texts were composed in Old English between the beginning of the seventh-century (~600) through the end of the eleventh-century (~1066), approximately. Scholars often use the date of the Norman Conquest of England in 1066 as the boundary between the use of Old English and Middle English, and Middle English is used in texts composed after this, from the end of the eleventh-century (following the Norman Conquest) to the beginning of the sixteenth-century. From around 1500 to 1550, a major shift in the pronunciation of vowels in English occurred, and its completion marks the beginning of the use of Modern English. Therefore, when Jane Austen begins writing at the end of the eighteenth and beginning of the nineteenth-centuries, we are well within the era of the usage of Modern English. When you read her works, you will see that, for the most part, although some meanings have changed, she is generally easy for a twenty-first-century reader to understand, especially compared to works written in Old English (which reads, frankly, like a completely different language!).
https://en.wikipedia.org/wiki/Middle_English

https://en.wikipedia.org/wiki/Modern_English

https://en.wikipedia.org/wiki/Old_English