Audacity 3.7.x does obviously not like earlier projects (that is what I’ve learned in this forum). Therefore you should open any project file with the version which you used to create it.
Well, if you moved them - how should Audacity know where they are? You can try double-clicking the project file, this should invoke Audacity and load the file. Or you can use the “Open…” command in the menu and search for the file in your directories.
Did you not export a sound file of your work (WAV, AIFF, or any other lossless format)? You should really do this.