Certified GKH Gardening Expert
It looks good. Many factors can be considered regarding your blackberry plant. If the plant is still too young, it may just need more time. If the plant is stored in that container outdoors, the newly formed flower buds may be injured from cold weather. Or, if you leave the plant indoors, it may not receive enough dormancy or "chill hours" to set buds. Also, if you have pruned the plant annually, it may have been at the wrong time.
For more information on blackberries, please visit this link: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberries-not-fruiting.htm