In the last couple of days, 5/9/18, I upgraded to the new LR version.
It has split all EXIF data to a sidecar file, which to my knowledge I did not consent to.
Now I cannot open my files in this 'upgrade' version.
"Upgraded"- how? (by download or Desktop App)
Your Operating System Version Number?
"new LR version" - Details please, Copy and paste top 10 lines from the Lightroom Menu: Help > System Info...
"split all EXIF data to a sidecar file" - In Catalog Settings/Metadata - is there a check mark in the option?
(With the option un-checked 'off') XMP sidecar files can be deleted (in bulk in the OS) if wanted. All EXIF data remains recorded in the Lightroom Catalog (not split apart!).
Is it possible you used the keyboard shortcut [Ctrl+S] to 'Save' metadata at any time?
"cannot open my files" - why? What error message? "Open" from where & how? What Camera & Model number? Are they in the Catalog?