You can find forgotten subscriptions without connecting Gmail or Outlook. Use a bank or card statement and the Apple Subscriptions list. That is the right path for a work inbox, a shared account, or iCloud Mail (which third-party apps cannot OAuth into).
Statement first
Download 90 days of PDF or CSV from the card that actually pays. Recurring names and amounts are the subscriptions. Unwanted Subscription reads the PDF, matches known brands, and lists unknown repeaters. CSV never leaves the phone. Details: how it works and privacy.
Then Apple
Settings, your name, Subscriptions. That catches App Store trials, iCloud+, Music, TV+, and Arcade. Deleting those apps does nothing. Cancel Apple subscriptions.
When mail still helps
Ugly card descriptors are easier to name when a receipt exists. If you can connect a personal Gmail later, do. If you cannot, name the repeater from memory or the merchant’s own site. You do not need a perfect ledger to cancel the expensive ones.