If I buy a 50gb plan and unsubscribe after 1month will that 50gb available or not?

Quick answer, no, it will not be there.

Click on the link to read what happens when you "Downgrade or cancel your iCloud storage plan" on an iOS device, a Mac, or a PC. --> https://support.apple.com/HT207594

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"What happens when you decrease your storage plan

When you downgrade your iCloud storage plan, the storage decrease takes effect after your current monthly or annual subscription ends.

If you downgrade or cancel your plan and your stored iCloud content exceeds your available storage, new photos and videos don’t upload to iCloud Photos, files don't upload in iCloud Drive, Messages in iCloud don't update, and your iOS devices don't back up. Learn how to manage your storage by deleting the information that you don't need anymore.

If you downgrade to the free iCloud Storage plan, you'll have 5GB of storage."

Not only will it revert back to 5GB but your data will be purged to get your used storage back below that free limit. So if you do cancel or just stop paying, make sure you transfer data to somewhere else or you will lose it.

It costs a company money to provide cloud storage, so nobody offers much of it for free.

When people cancel a subscription, they get an email saying they have 30 days to transfer their data for safe keeping, after which data will be purged to fit within 5GB. Since that’s the normal message received when canceling a subscription, I cannot imagine that a delinquent account just sits untouched forever.

And the iCloud terms of service do include the clause that they always have the right to delete content.

Legal - iCloud - Apple

“If Apple is unable to successfully charge your credit card or payment account for fees due, Apple reserves the right to revoke or restrict access to your stored Content, delete your stored Content, or terminate your Account.”

Sandeepsahu wrote:

If I buy a 50gb plan and unsubscribe after 1month will that 50gb available or it will be not there after unsubscription?

If that worked, nobody would pay past the first month.

I hadn't see anybody mention the first, thanks.

About the terms, they probably do use that clause although if you downgrade to free then they shouldn't be trying to charge your card. It's a gray zone.

Apple doesn't actually say it will be purged, they just say you can't add anything more.