Q.Is it true not ALL ZINNIA SEEDS WILL BLOOM?
I GROW ZINNIA FLOWERS BUT THIS YR I DECIDED TO KEEP 100 DRIED FLOWER BUDS, AND TOOK OUT THE SEEDS TO PLANT NEXT SPRING. I later found out that not all seed producing zinnias will grow from the seeds they produce. Is that true and, if so, which zinnia flowers will grow from their seeds?

Certified GKH Gardening Expert
It isn't that they won't bloom, though some might not. It is more that they won't be anything like the parent flower. There is quite a bit of genetic variation and hybridization in modern cultivars.
If you want some true to seed, you will need to look into planting heirloom varieties. They will, usually, breed true.
Here is an article that will help you to care for the plant: https://www.gardeningknowhow.com/ornamental/flowers/zinnia/growing-zinnia-flowers.htm