GraphQLResolverMap no longer includes GraphQLScalarType

I am upgrading from Apollo 2 to 3 (long overdue, I know) and while I’m at it, I also bumped graphql from 15.6.0 to 16.6.0.
My compiler is spitting out errors that I traced down to the GraphQLResolverMap no longer accepting GraphQLScalarType. Even Apollo’s own example of a custom scalar doesn’t compile. What am I missing?
I can get by the compiler error with a //ts-ignore and my server behaves as intended (so far) but that doesn’t sound like the right way forward. Is there a library I am missing?

"@apollo/federation": "^0.38.1",
"@graphql-codegen/typescript": "^3.0.4",
"@graphql-codegen/typescript-resolvers": "^3.2.1",
"@playlyfe/gql": "^2.6.2",
"apollo-server-core": "^3.12.0",
"apollo-server-express": "^3.12.0",
"express": "^4.18.2",
"graphql": "^16.6.0",
"graphql-tools": "^8.3.20",
"@graphql-tools/utils": "^9.2.1",
"graphql-type-json": "^0.3.2",

Node v 20.1.0, typescript 5.0.0