This is probably not a software bug we can fix in enigma2. It's one of:
1. The USB enclosure's bridge chip (JMicron, Realtek, ASMedia etc.) doesn't advertise UNMAP support, or needs a firmware update
2. The SF8008 kernel doesn't have USB discard support enabled for this bridge
3. The UAS vs usb-storage driver, UAS is required for TRIM over USB to work in most cases
Please run these two in terminal and post the output:
dmesg | grep -E "uas|usb-storage|sdd"
cat /sys/block/sdd/queue/discard_granularity