That's... A lot of storage. I'd say your options are, in no particular order:
- buy a 12 bay NAS.
- expansion unit. Do it as a separate volume and shuffle cold data onto there.
- upgrade the drives.
Failing that you could just have a bit of a purge? If not straight deleting stuff, move things onto an external drive.
You could also try deduping. There's a script that'll add any drive to the internal "supported" list and also enable dedupe on mechanical drives. The savings were minimal on mine but you might have more luck. https://github.com/007revad/Synology_enable_Deduplication
There was plenty of demand when fuel prices shot up a few years ago, but since then, unless you have access to off street parking and your own charger, it's become more expensive to drive an EV than a combustion car.
When the price of oil goes up the government falls over itself to subsidise and bring it back down. When the price of energy goes up they shrug their shoulders and slap 20% VAT on public chargers. It's insane and hardly any surprise that demand has "flagged".