Hi Henri,
Nice to see you as well.
Yes, I checked it in R21 as well, as usual, I do not post here based on my memory: Things might change.
Speaking of changes: IF you create a new scene in R23, you will see that the Viewport Render option in the Render Settings will give you a different result. Different from opening an older scene from a previous version that had Hardware Render enabled.
The current settings are more defining the words clearly. Viewport works for Viewport, but the Render Settings’ Filter is purely for the Picture Viewer.
I hope with all this, as confusing as it might be right now, I hope to clear it a little bit.
Have a wonderful evening.