The Grail is a gravel bike and the Endurace is a comfort-oriented road bike. There are multiple differences between the two:
Geometry: The Grail is a longer bike with a longer wheelbase to generate more stability when riding off-road. The Endurace has a slightly shorter wheelbase for more agile handling on the road.
Tyre clearance: The Endurace comes with slick road tyres. It has 30 mm tyre clearance enough for light gravel tyres. The Grail comes with 40 mm gravel tyres that provide plenty grip and traction off-road.
Gearing: The Endurace comes with gearing optimised for road cycling. This means the gaps between ratios are smaller and that you have bigger gears at the top end for faster top speed. However the lightest gears aren't as light as on the Grail. The Grail’s gravel-optimised gearing gives you easier lighter gearing ratios for the kind if steep climbs you more often find off-road. The limitation is that your biggest gears are not as big as on a road bike limiting your absolute top speed.