2016 - "Don't Skype & Type! Acoustic Eavesdropping in Voice-Over-IP" - https://arxiv.org/abs/1609.09359
2020 - "Behavioral Acoustic Emanations: Attack and Verification of PIN Entry Using Keypress Sounds" - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7309150/
Maybe they mean this one...
2023 - "A Practical Deep Learning-Based Acoustic Side Channel Attack on Keyboards" - https://arxiv.org/abs/2308.01074