relationloadstrategy with planetscale and prisma

Question

As far as i've noticed it should be possible to add relationLoadStrategy to Prisma when using planetscale since it works with MySQL. but for some reason i cant make the option to show up.

I figured it's got something to do with Foreign key columns. can anybody tell me how to implement that?

i added this to my schema.prisma:

generator client {
    provider        = "prisma-client-js"
    previewFeatures = ["relationJoins"]
}

but still don't have the option in my query call