I believe it will only show magnetic north. You can also set up numerous data pages and have one field set to bearing.
Response from ViewRanger Support:
We use true north if it is available (i.e. the device has a GPS position), magnetic north if there is no GPS position.
We don't offer a way to read the compass bearing, I will note that on our wish list.
If following a route or navigating to a point, we do offer a bearing in the configurable values, to the target waypoint or POI. That bearing uses grid.
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SectionHiker: Who uses the OS app? They have bearing printed at the bottom of the screen...seems a lot less complicated than View ranger.