Can I still prune basil after it flowers?

Yes, you can still prune it. Pinch or snip the flowering tip just above a healthy pair of leaves or a node. That can encourage side shoots, and you don't need to cut back every leafy stem. The plant is still usable.

Don't expect a big change overnight. New growth can start as tiny leaves, and a few days may not be enough to see much. Keep an eye out for more flower spikes and pinch those off if you'd rather encourage leafy growth.

If you want to save seed, leave a few flower heads instead of removing every one. Otherwise, trim the flowering tips back to a leaf node. Some gardeners remove them because they prefer the plant's leafy growth and flavor before it flowers.