Does anybody know the name of this setting inside of VS Code Insiders? For grayed out parameter and variable annotations

Those are Inlay Hints. You can enable (the default) or disable them with the setting:

Editor > Inlay Hints: Enabled

or change the Font Family or Font Size by searching for Inlay Hints in the Settings UI.

And there is finer control for parameter names/types, variable types and more for js/ts files.

For a lot more, see the release notes v1.60 release notes:

The most significant new tooling feature in TypeScript 4.4 is inlay hint support. Inlay hints add additional inline information to source code to help you understand what the code does.

Parameter name inlay hints for example show the names of parameters in function calls:

This can help you understand the meaning of each argument at a glance, which is especially helpful for functions that take Boolean flags or have parameters that are easy to mix up.

To enable parameter name hints, set javascript.inlayHints.parameterNames.enabled or typescript.inlayHints.parameterNames settings. There are three possible values:

none — Disable parameter inlay hints. literals — Only show inlay hints for literals (string, number, Boolean). all — Show inlay hints for all arguments.

In addition, VS Code also offers inlay hints that show implicit type information in your JavaScript and TypeScript code.

Variable type inlay hints show the types of variables that don't have an explicit type annotations.

Settings - javascript.inlayHints.variableTypes.enabled and typescript.inlayHints.variableTypes.enabled

[And more at the release notes link.]