Can one increase iCloud storage > 2Tb ?

Yes sure.

See this Apple article: Upgrade to iCloud+ -> Upgrade to iCloud+ - Apple Support

See also: iCloud+ plans and pricing -> iCloud+ plans and pricing - Apple Support

If you have upgraded iCloud storage, it would take about 1 to 3 business days in order to process.

Once your request for iCloud+ has been activated, you should receive an invoice in your email box.

See also the following Apple articles:

Check your iCloud storage online or on any device

Check your iCloud storage online or on any device – Apple Support (UK) 

How to use iCloud on iPhone

How to use iCloud on iPhone – Apple Support (UK)

Manage your iCloud storage

Manage your iCloud storage - Apple Support

Niel wrote:

Sign up for both Apple One and a standalone iCloud+ plan. The maximum is 4TB.

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This is the only way.

From here: link-> What happens to your iCloud storage when you sign up for Apple One - Apple Support

If you need more iCloud storage

After you subscribe to Apple One, you can buy more iCloud storage if you need more. With both Apple One and an iCloud+ plan, you can have up to 4TB of total iCloud storage.

Sign up for both Apple One and a standalone iCloud+ plan. The maximum is 4TB.

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Sorry, didn't read carefully.

No, that is not possible, 2 TB is the maximum.