USB drive just as good as tape.
Tape is only secure against encryption, because it is offline.
USB drives can be offline too, if you remember to take it out. USB drives only “get lost and nicked” because they are small, cheap, and widely used and usable as transfer media.
I think your problem could be solved by buying a bunch of normal USB drives, and fixing each in a large clumsy plastic box painted in puce/khaki stripes, and labelled “Tape”. Put an oven timer in each box to remind you when to attach and detach it for backup. Ta Da!