How do you reapply sunscreen? Would it be okay to just use an SPF 50+ cushion instead of sunscreen?

How do you all reapply sunscreen? Since I apply a 15% Vitamin C serum in the morning, I always make sure to apply sunscreen when I go out. However, I've heard that it's better to reapply it once or twice throughout the day rather than just once...

The problem is, I don't know what to do when I try to reapply sunscreen after having already applied sunscreen and cushion foundation in the morning. I can't remove all my makeup to reapply it, but if I just apply sunscreen over my existing makeup, it smudges or looks cakey. Since I'm just reapplying it without completely removing everything, it ends up looking thick.

So these days, I'm wondering if it's okay to reapply an SPF 50 cushion foundation just for touch-ups. Since cushions offer UV protection, I'm curious if this method is sufficient, or if it's better to properly reapply sunscreen. I'm also curious how those who actually reapply sunscreen multiple times a day manage to do it over makeup. Please recommend any good methods or products you use!