How to get high quality PNG files under 10MB?

Hello, my designs are very colorful and detailed - and if I cut them out in Photoshop with 4000x4000 pixels and save them as PNG, they are almost always larger than the 10MB allowed. Of course I can compress the PNG from 24 to 8 bits - but unfortunately the quality massively suffers.
How do you solve this problem that you can’t get high-quality designs in PNG format with transparency in 10MB?