A very easy way to add new financial dimension selection values in “Use values from” list in Financial dimension configuration in Microsoft Dynamics 365 for Finance and Operations.

Create a new view, View name must be DimAttributeYourTableName in my case “DimAttributeOpportunityTable” and the data source name as BackingEntity with 3 fields Key(Recid),Value(OpportunityId),Name(Subject) and indexes on Value not duplicate and Name allow duplicate with the below mandatory properties of the view,

1. Label
2. Singular Label
3. Title Field1
4. Title Field2
5. Configuration Key (same as of the table in view)

once the view is done call the delegate method registerDimensionEnabledTypeIdentifiersDelegate of class DimensionEnabledType to register your view in the list.

public class DimAttributeOpportunityTable extends common
{
[SubscribesTo(classstr(DimensionEnabledType),delegatestr(DimensionEnabledType,registerDimensionEnabledTypeIdentifiersDelegate))]
public static void registerDimensionEnabledTypeIdentifier(DimensionIEnabledType _dimensionEnabledType)
{
_dimensionEnabledType.registerViewIdentifier(tablestr(DimAttributeOpportunityTable));
}
}

also extend delete and update methods of the table mentioned in the view,

[ExtensionOf(tableStr(SmmOpportunityTable))]
internal final class SmmOpportunityTable_Extension
{
public void delete()
{
    next delete();
    if (!DimensionValidation::canDeleteEntityValue(this))
    {
        throw error(strFmt("@SYS134392", this.OpportunityId));
    }
    ttsbegin;
    DimensionAttributeValue::updateForEntityValueDelete(this);
    ttscommit;
}
public void update()
{
    Common originalRecord = this.orig();
    next update();
    DimensionValueRename::syncRenamedValue(this, originalRecord);
}
}

Once above is done it will show in the dropdown list of the financial dimensions,

Thanks,

Happy Daxing with Rizz.