While it's often been claimed that Germany lost World War II because of Hitler's interference in military planning and he should've left things to his generals, the reality was more complicated than that. There were times when Hitler was right and his generals were wrong, and one of these times was Operation Citadel, which started the famous Battle of Kursk. Hitler had severe reservations about the plan, even commenting that thinking about it made him sick to his stomach, but reluctantly approved it... and it was a major Soviet strategic victory, validating Hitler's misgivings.
So what if Hitler had trusted his instincts and refused to give the green light?
problem is on the face of it attacking and defeating the red army at Kursk potentially ticks too many boxes on the German check list for them not to do it:
1). A decisive engagement that puts the German army back on the front foot which is where it needs to be to achieve any of its war aims.
2). Allows them to utilize the German offensive ability and advantages to carve into an apparently badly positioned more static enemy
2). It's a way out of a war of attrition with the USSR. that is already 18 months behind schedule and showing no other likely routes to victory
3). Ending the threat in the east in 1943 allows them to bolster the west where clearly the wallies are making moves.
4). It's the old Barbarossa plan find and defeat the Red army anyway, and the Red army has apparently obliged.
5). A proper decisive head to head of ideologies made flesh, crank up the Wagner and demonstrate Nazi/aryian superiority over judeao-boshevism, now the enemy has stopped lurking behind logistics issues, urban warfare and winter. After all the German army was able to destroy massive Red army formations out in the open in 1941 whenever they met them by being better right?
Of course it's not 1941 it's 1943, the red army isn't the red army of 1941 and neither is the German army it's 1941 self
But the main issue with Hitler vetoing it is what else are they going to do? If you've invaded a country and can't fight it's army, what's your plan?
Unless Hitler thinks he can arrange a better situation to defeat the Read Army in than the one presented at Kursk the future is just more of the same as has been happening, them getting slowly pushed out of the territory they took in 1941 by attrition. All the while the US is ramping up mobilization and resources, the bombing campaign over Germany is increasing and in July the wallies will have invaded Sicily and pretty soon after that Italy and so on.
So the real question isn't just "what if Hitler vetoes Citadel?",
it's:
what would he veto it in favor of that at the time of the decision would look better for him than Citadel