Unfortunately, Premiere Elements projects created on Windows system will only work on windows. For MAC, you will need to create a new one.
As John Nash points out, project files (project.prel files) created in Premiere Elements Windows will not work in Premiere Elements Mac and vice versa.
Projects taken to completion in the program/operating system in which they are created is the way to go.
If at all practical and depending on the "need to do" feature, you might export the Premiere Elements Windows Timeline to a .mov or .mp4
file and then import that into a new Premiere Elements Mac project. The level of edits in Premiere Elements Mac would dictate the degree of cutting of the Timeline content in order to accomplish the wanted edits in Premiere Elements Mac.