Only one capability depends on the connection: discovery. A linked app reads your transaction history and groups the repeating charges, which is how it surfaces the subscription you had forgotten about. Nothing you type into a manual tracker reproduces that, because the tracker knows only what you tell it.
Everything else survives the constraint. Renewal dates, trial deadlines, monthly and annual totals, reminders before a charge lands, and step-by-step cancellation instructions all work from entered data. So does the cancellation itself — unless you pay for a concierge that contacts merchants on your behalf, you were always going to be the one clicking through the provider's own flow.
The practical workaround for the discovery gap is to do it once, by hand: pull 6–12 months of statements, list every recurring charge, and enter the survivors into whichever tracker you pick. After that the tracker keeps up on its own, because every new subscription is one you knowingly signed up for. The method comparison is at /best/best-ways-to-run-a-subscription-audit, and the step-by-step process at /blog/how-to-do-a-subscription-audit.