C# Logical and Math expression parser
I can see three small improvement areas:
Use ctor instead of object initializer
Instead of this:
new DataColumn(v.Key) { DataType = v.Value.GetType() }

Use this:
new DataColumn(v.Key, v.Value.GetType())

Object initializer will run after ctor. If ctor accepts that parameter then prefer to provide it in the ctor.
Use early exist instead of guard expression
Instead of this:
if (Variables != null)
{
    computer.Columns.AddRange(Variables.Select(v =&gt; new DataColumn(v.Key, v.Value.GetType())).ToArray());
    computer.Rows.Add(Variables.Values.ToArray());
}
return computer;

Use this:
if ((Variables?.Any() ?? true)) return computer;

computer.Columns.AddRange(Variables.Select(v =&gt; new DataColumn(v.Key, v.Value.GetType())).ToArray());
computer.Rows.Add(Variables.Values.ToArray());
return computer;

Yes, I know it's against the single return statement. But with this approach you streamline your logic.
Use immutable collection instead of just readonly access modifier
Instead of this:
static readonly Dictionary&lt;JTokenType, Type&gt; conversions = new Dictionary&lt;JTokenType, Type&gt;()
{
    [JTokenType.Integer] = typeof(int),
    [JTokenType.Float] = typeof(float),
    [JTokenType.Boolean] = typeof(bool),
};

Use this:
static readonly ImmutableDictionary&lt;JTokenType, Type&gt; conversions = new Dictionary&lt;JTokenType, Type&gt;()
{
    [JTokenType.Integer] = typeof(int),
    [JTokenType.Float] = typeof(float),
    [JTokenType.Boolean] = typeof(bool),
}.ToImmutableDictionary();

With readonly you only prevent to replace the whole object. But you can still add and remove new items to the dictionary:
//Invalid operations
conversions = null;
conversions = new Dictionary&lt;string, JTokenType&gt; {};

//Valid operations
conversions.Add(JTokenType.Array, typeof(Array));
conversions.Remove(JTokenType.Integer);

With ImmutableDictionary the Add and Remove will return a new ImmutableDictionary so it will not have any effect on the original collection. Visual Studio will even worn you about it: