Update 22. november 2022:
As @tracernz writes in a comment the current best practice to make an airport work with autotuning ILS is the following:
Keep deleteAllILSs="FALSE" and use IlsReference instead of configuring an ILS from scratch. This allows the airport to load default navdata correctly.
This is how it can be set in the scenery editor:
This is how this is inserted in the xml file if you prefer (but you probably shouldn't):
Old info from early 2021 in case it's still needed by someone:
I have spent too many hours trying to get this to work properly. Setting up a properly working, autotuning and correctly offset ILS was for a long time impossible, but it seems to work after the latest patches. This way works for the airports I have tested it at (ENZV, ENBR, ENBO, ENSH).
These instructions assumes you are already experienced with the scenery editor and editing an airport.
Note that the ILS heading is currently magnetic, corrected with the in-sim Magvar value. This in-sim Magvar value does not seem to correspond to IRL magvar, and the sim seems to ignore the magvar you set in airport properties (but not the runway properties). This means you can't use the magnetic heading values directly from the charts or AIP info, at least for the airports in Norway I have set up.
For a simple setup you could just read the compass heading in your plane when aligned with the runway and use this value for ILS heading, but +/- 1 degrees can be very noticeable on approach.
1: Position your plane at the airport and use simconnect to measure the magnetic deviation at the airport in the sim with the simconnect variable "MAGVAR".
2: Load your project in scenery editor. Go to properties for the airport object and tick the box deleteAllILSs.
3: Check real world AIP or charts for any ILS offset.
3: Do some math:
a: <RunwayHeading> = The runway heading set in runway properties
b: <ILSHeading> = <RunwayHeading> - <magvar>
c: Adjust the <ILSHeading> value by correcting for the offset in the AIP / charts.
4: Go to Runway properties, to the ILS options and input <ILSHeading> into the heading field for the ILS.
5: Calculate 360 - <magvar> and input this value into the magvar field for the ILS.
6: Fill in the rest of the fields and position the Localizer, Glide path and DME transmitters correctly. Remember to check the Z-axis, not just the X and Y axis for the position!
7: Hope MSFS doesn't update the magnetic deviation data or start using the magvar field in airport properties.
ENBO - Bodø airport ILS 25 is 10.2 degrees offset from runway heading.
In real life:
ILS heading 261.6 degrees with magvar 6.4 degrees east.
Runway heading 257.8 degrees. Measured magvar through simconnect 3.993 degrees, rounded up to 4 degrees.
ILS heading = 257.8 - 4 + 10.2 = 264
Magvar = 360 - 4 = 356