Is it possible to create memory-optimized M1/M2 VMs in Google Cloud Engine with custom vCPU and Memory allocations? The chart here lists pricing by vCPU / Memory allocated, suggesting it might support custom allocations. But there is no option to create a custom memory-optimized VM in the VM creation UI.
Unfortunately it's not possible at the moment. Please have a look at the documentation Creating a VM Instance with a custom machine type:
Custom machine types are available for general-purpose machine types only; that is, when you create a custom machine type, you are effectively deploying a custom machine type from the E2, N2, N2D, or N1 machine type family.
So, it's expected that there's no such option via GCP Console UI.
Meanwhile, you can file a feature request on the Google Public Issue tracker to change it.