If you have a system that is Windows 10 you can install it and then copy the Scratch 3 folder contents to a thumb drive and then copy/paste that folder into the Windows 7 system and get it working I have heard, but haven't tried.
I ran into a similar issue with software that dropped support for Windows XP that would refuse to install to XP, yet i could install the software to a Windows 7 system and then copy the folder contents of it to thumb drive and copy paste that to the Windows XP system for the 32-bit version of software.
Running it on Windows 7, if it works, would be at your own risk for projects getting corrupted or crashing.
Here is another source that hints on it working on 7 when performing the install to 10.
Requirements Windows 10 writes but works in Windows 7
https://scratch.mit.edu/discuss/topic/326861/?page=38