By default, the results folder storing all run outputs is created next to the project .mlxtran file and has the same name as the project. It can however be changed via the Monolix menu: Settings > Project settings > Result folder:
When clicking on the path, a pop-up file browser window allows to manually choose another folder. All results will be put in that folder (without creation of folder with the same name as the project).
Note that the given path will be overwritten by the default location when doing a “save as” (but not when doing a “save”).