Corrupt file

Your attachment opened fine for me in MuseScore 3.
I saved it in MS3 and here it is:
Hey_jude-MS3.mscz
It should open in MS3 and in MS4.

I don't think so, in this case.
However, I changed the z in the extension to an x and tried to open the file. I got a corrupt file message. I selected the details button and got an error message. You can do this and google the message. Maybe it will help.
Other than that, you might look in your backup folder (in the scores folder) for a saved version. This is an invisible folder. You'll need to Google "how to view hidden folders".
I learned long ago two important things.
1. Never save to the cloud.
2. Always do a "save as" with a new version number after every session with a score. Never just a save.

Your attached score Hey_judeV4.mscz was written and last saved with MuS 3.6.2. And it can be opened in 3.6.2 without any problems.
If you have a problem with the MuS 4 file version, you should attach the version you saved with MuS 4.

After installing MuS 4, double-clicking on the file will always start MuS 4. If you want to open it with MuS3, start MuS 3 and use "Open file" there or drag the file from Windows Explorer into the MuS 3 window or right-click on it and use "Open with" in Explorer. (This applies to Windows - you have not said which operating system you are using)

If you have installed both MuS versions, please note that the scores are stored in different folders by default. It is ".../Documents/MuseScore3/Scores" or ".../Documents/MuseScore4/Scores". If you open a MuS 3 score with MuS 4, always use 'Save As' to save it in the MuS 4 version in ".../Documents/MuseScore4/Scores" so that both file versions are preserved.