If you've got a lot of data that does not need the speed of a SSD, you could consider an external desktop hard drive. Those are available in capacities up to about 20 TB or so.
Even bus-powered notebook hard drives come in capacities of up to 5 TB.
Whatever you use for primary storage, be sure to get additional drives for backup.
If you want to choose your own internal drive mechanism (e.g., to be sure that you got a drive mechanism that uses Conventional Magnetic Recording (CMR), and not Shingled Magnetic Recording (SMR)), you could get an enclosure like this one and (with a bit of care) install your own drive mechanism.
https://eshop.macsales.com/shop/owc-mercury-elite-pro
OWC sells this either as an enclosure, or with a hard drive pre-installed. (I don't know whether the drives they pre-install are CMR or SMR.)