This is intentional. Particle effects are intentionally turned off for Bad Omen (it whould be silly if it wasn't imo), and the icon is there to let you know you have bad omen.
I don't really know what you're tryna point out here, but items despawn after 5 minutes (when the chunck is loaded where the items are in) of them laying on the ground. When you die, all your items are dropped so they then the despawn timer of 5 minutes
This is intentional. Particle effects are intentionally turned off for Bad Omen (it whould be silly if it wasn't imo), and the icon is there to let you know you have bad omen.