Just upgraded to Ubuntu 18.04 and can't use compiz grid window resize commands?

Ubuntu 18.04 dropped support for the Unity desktop compositor in favour of GNOME Shell. GNOME Shell is incompatible with Compiz. You need to look for a method to replicate this behaviour using GNOME Shell and its extensions or install and use an unofficial, community-supported version of Unity.

P.S.: There's a follow-up question with a suggestion for a replacement GNOME Shell extension.