sketch won't properly transfer to laptop

Change of the file name could be due to an over eager virus scanner trying to protect you from executables downloaded from the web.

I did try turning off all protections from MalwareBytes but that made no difference. I think there's another protection type program I can try that with.

It's an old computer but new to me.

You can creates a portable version that requires no 'installation' and just copy the files.