Online Data Storage Plans

I have 4 TB data to backup to the cloud.
I have an iCloud, Microsoft and a Google account.
As far as I can tell, my iCloud account is the only account that will let me easily upgrade to 6 TB of space. With Google and Microsoft, I have to pay for extra accounts and each extra account is limited to 1 TB of storage.
Can anyone else suggest another cloud service?

Did you truly need JUST backup. (As in you hope to never access the data?) If so, something like Amazon Glacier is very cheap for large amounts of storage. It gets quite expensive if you need to restore it though. (And it can also be slow, thus the name.)

Otherwise, something like Backblaze may work. They have “unlimited” I think… but from one PC.

Google does offer additional storage for purchase. I believe you can add 2 TB to the free amount.

Thanks guys.
I will need to share some of the directories.
So I’ll stick with iCloud.