Hi @Sanu ,
Could you please share a bit more about your scenario?
Do you want to only display the "Parkering" room in your 'Book a Room' template app?
If you want to only display the "Parkering" room as available room in your 'Book a Room' template app, I think the Filter formula you specified is correct. Please modify the formula within the OnVisible property of the RoomSelectScreen as below:

Please note that, the OnVisible property of the screen would be fired only when you switch from another screen to current screen. So please consider save your canvas app, and then re-load your canvas app, then check if the issue is fixed.
Note: Please make sure you have fired the OnVisble property of the RoomSelectScreen in your canvas app properly.
Regards,