Does Apple do this often? I've always wondered if iCloud is worth getting, given that it constantly spams me to use it with my iPhone
They do have phone support, but they refused to unlock the account and just said she'll never be able to use primary email account with Apple's systems because of the frozen account.
So yes, any cloud provider can lock you out for arbitrary reasons. Just because they answer the phone doesn't mean the customer support agent can actually do anything about it.
Photos sync to iCloud is terrible slow though compared to Google Photos - syncing 100GB take days and 500GB takes forever. At least it end-to-end encrypted with Avanced Data Protection. But yeah if you multi-TB photo archive buying large storage options of iCloud make no sense simply because it's impossible to use.
I'd better use self-hosted Immich.