There have been several claims for the "longest sentence in the English language" revolving around the longest printed sentence.
Sentences can be made arbitrarily long in various ways. One method is successive iterations, such as
"Someone thinks that someone thinks that someone thinks that..." while another method is combining shorter clauses. Sentences can also be extended by recursively embedding clauses one into another, such as:
"The mouse ran away."
"The mouse that the cat hit ran away."
"The mouse that the cat hit that the dog bit ran away.
"The mouse that the cat hit that the dog bit that the fly landed on ran away."
...
This also highlights the difference between linguistic performance and linguistic competence, because the language can support more variation than can reasonably be created or recorded. As a result, one linguistics textbook concludes that, in theory, "there is no longest English sentence."
Solar Bones by Mike McCormack is written as one sentence. It won the 2016 Goldsmith's prize for experimental fiction, was longlisted for the Booker in 2017 and won the 2018 International Dublin Literary Award.
Ducks, Newburyport by Lucy Ellmann, a finalist for the 2019 Booker Prize, runs more than a thousand pages, mostly consisting of a single sentence that is 426,100 words long
This Book Is the Longest Sentence Ever Written and Then Published (2020), by humor writer Dave Cowen, consists of one sentence that runs for 111,111 words, and is a stream of consciousness memoir.