Postgres built up a whole separate infrastructure for BLOB storage, with a streaming API in/out of BLOBs et al; but after landing the TOAST-table logic, it became basically† obsolete—you can just use a regular TEXT or BYTEA column to achieve the same things now.

† BLOBs are still relevant in the cases where you have such huge data in each BLOB that you need to work with it in a streaming manner. But people don’t tend to build systems with this concern (i.e. object stores) on top of RDBMSes, so it’s pretty darn rare that anyone actually turns to Postgres’s BLOBs to solve a problem in practice.