According to new documents apparently filed with the World Intellectual Property Office (WIPO), ASUS has designed a phone along the lines of the Xiaomi Mi Mix 3. However, this version may be able to slide out from the bottom of the phone as well as the top.
https://www.notebookcheck.net/ASUS-allegedly-patents-a-dual-slider-phone.421421.0.html
I remember the nokia N95, had dual slider function first.