Is one allowed to make a temporary wall on Shabbos from a blanket to separate one side of a room from another?
It depends on the reason that the temporary wall is being made. If it is in order to halachically separate the two sides of the room, in order to permit doing something because now it is on the other side (called a mechitza hamateres) then it is forbidden. For example putting up sheet in order to permit marital relations, or to permit someone to walk in front of someone davening shemona esrei. However if it being made for other reasons it is permitted. Placing a blanket between men and women in order to daven is controversial if it is considered called a mechitza hamateres or not. Most poskim hold that it is permitted because it is only needed there so the men won’t see the women, but not because they halachically have to be in a different domain.
Rema 315-1, Ohel Aray 11-4, Oz Nidberu 13-9, Kitzur Hilchos Shabbos 37 ftnt. 36, Orchos Shabbos 9-39, Piskei Teshuvos 315 ftnt. 39, The 39 Melachos Boneh ftnt. 178, The Shabbos Home 2 pg. 439 ftnt 21.