Can I sell Psd files after using the starter assets in Adobe Dimmension

yes you can sell a image made of starter assets or with some starter assets included... the copyright is complex but basiclly your image is yours unless you are somehow saying that these starter assets are made by you or the main point of the file

for exmple; if you put your sister on a t-shirt with a starter square in the background then clearly your sister is the point of that T-shirt... if you just had the square it could be agued the asset is the point but even then its hard to see a copyright case being made against you