Paddling a SUP upwind in greater than 20kts can be a pain, unless you’re doing it intentially to train for fitness or a race. If you’re unwilling or physically can’t sit and paddle your board like a canoe, then the most effecient method is a sailing technique called Tacking.
Tacking is essentially padding upwind in a zig zag pattern going diagonal to the wind. Tacking takes longer but prevents your body from acting like a sail trying to go upwind. By paddling diagonal, your body is going sideways reducing windage. You can do intentional diagonal angles or just let the board turn itself after paddling on one side after a few strokes, then switch hands to the other side.
While doing so, feather your blade when returning it to the catch. When you remove the blade from the water after a stroke, rotate your wrists forward which flattens the blade face so it returns to the nose parallel to the water’s surface cutting through the wind. Always twist your torso for your forward stroke to increase power and reduce fatigue.
Another method to reduce wind shear is to stand in a quasi surfer’s stance where your body faces upwind in a 45 degree angle while paddling straight or tacking. Always use your leash in wind above 20kts to prevent from losing the board in case of a fall.