Cannot open an .sdlproj file

I have an .sdlproj file I created myself and now I can't open it. I get a message that my program edition doesn't support this type of files and only single projects or project packages can be opened. I don't really understand why this is because all the other files I've translated and saved before have the same sdlproj extension. I translated this particular document on another machine and am now trying to open it on my other laptop. On both I have Trados Studio 2021. Can anyone help, please? Thank you.