Thumb drives.
Financial stuff, copies of legal documents, large libraries of PDF books, reports, etc., etc.
And then back the main drive up to FOUR thumb drive backups.
Reasons:
(1) USB drives are huge now. (2) Convenient - can move from one PC to another easily. (3) Convenient - I do NOT have time to mess with other solutions. (4) Safety - valuable financial stuff almost always OFFLINE reducing hacker vulnerability. (5) All PCs eventually fail - I'm old and have a collection in my basement - plus I have two fairly new ones awaiting repair in my home office right now.
Only disadvantage - I do have multiple legal copies of Microsoft Office on multiple PC to make moving thumb drives around practical.