Can't create a direct active relationship ... ambiguity between tables (Date table)

Hello Jop1235123,

Can you please try the following:

1. Use Userelationship in Your Measures

SumOfOrdersByYearReady = 
CALCULATE(
    SUM(Orders[OrderValue]),
    USERELATIONSHIP(Orders[YearReady], 'Date'[Date])
)

2. Creating a Disconnected Slicer Table

YearTable = DISTINCT ( SELECTCOLUMNS ( 'Date', "Year", YEAR('Date'[Date]) ) )

Then, you can use a measure to filter the orders based on the selected year from this new slicer

SelectedYear = SELECTEDVALUE ( YearTable[Year] )

OrderValueByYear = 
CALCULATE (
    SUM ( Orders[OrderValue] ),
    FILTER (
        ALL ( 'Date' ),
        YEAR ( 'Date'[Date] ) = [SelectedYear]
    )
)

Use this new measure in your visual instead of the direct column from the 'Date' table.

Hope this helps.