I am experiencing the same issue, I believe it started with the emergency patch 1.77.146.1030. Base game only, no mods/cc-never used.
Produce or flowers obtained from seed packets can't be sold via the inventory. Produce or flowers obtained via harvesting CAN be sold.
I am not certain if the quality makes a difference, but will update once one of the normal plants has something to harvest. At this point, I can sell harvested items from the inventory, but all of them in my save are evolved beyond normal. I did plant a normal seed, so once it produces something I'll test to see if there's a difference.
I purchased several uncommon seed packets via the planter box and through build/buy. None of the produce/flowers received from the packets can be sold from the inventory when trying to drag and drop them on the sell bar. They can be dragged to the ground or planter box and planted. I've tried dragging them from the ground to another sim's inventory and they are still unable to be sold.
Two workarounds: enable multi-select in the sims inventory and the items can be deleted, or place on the ground and sell in build/buy mode.
