bad exoport quality when working with gradients :/

hey, i wanna have a "fading-out" color in my corners, by creating a gradient that fades from purple to black (as in picutres to be seen). but whatever I do, when i see it in after effects the fadeout is in good quality, when i export its suddenly pixeled and i can the the edges of the decreasing color ... i tried everything that AI chatbots suggested, i work and export in 32-Bit, i have high quality formats (quicktime apple pro res 422 HQ), i made the pre composition huge for the object that has the gradient effect - nothing works... PLS id love the help. im going crazy here. spent way too much time on that already 😞 still new with after effects btw. lookin forward to any tipps!