I think you may have more difficult problems. I think Apple will dread the day they starting using Fusion drives. It appears that there are problems with Fusion drives and APFS which is required for booting as of Mojave. It also looks like you are already in Catalina by the main folder structure and definitely using APFS. I would Google Fusion drives with Catalina and see the problem. I actually uncoupled them for a friend with a 2015 iMac i7 with the 3TB Fusion. At least the 120GB SSD is big enough for a boot drive. You have a 28GB SSD and over 30GB of boot disk. But you are not even close as you need to account for the macS scratch disk which is essential for swapping out RAM as you change apps. I haven't had the time to read the entire thing as I haven't had that problem. Apple has to fix this, or you need to go back to High Sierra where the boot drive can be the old HFS+ file system. If there's a suit, you may end up getting a 256GB SSD. This is the same old problem of Apple making the consumer buy its products with half the technology and twice the price. Now they have advanced the technology for their new file system, but alienated almost everyone with a fusion drive. That's how I see it anyway.