The installer will find MSFS 2024 in the folder specified by the UserCFG.opt, same as MSFS 2020, just different location for the UserCFG.opt file.
We only had a small issue in the first release, where if the InstalledPackagesPath line in the UserCFG.opt file was empty for some reason, the Community folder couldn't be found but, we changed it and, in that case, the folder is assumed to be the "Packages" folder under the location where the UserCFG.opt file is located, which we verified is what is used in that case, so if you use the latest installer (just starting it will update it automatically), it should work even if your UserCFG.opt was in that state (never happened in MSFS 2020, must be an 2024-specific problem ).
Also, the simulator will automatically fix an UserCFG.opt with an empty InstalledPackagesPath string, so even before our update, running the sim again would have fixed the file just the same.