I clicked on Microsoft 365 in App Store and now it shows purchased. My intention was not to purchase it, how can I cancel? I cannot see subscriptions in App Store settings.

Microsoft 365 is free to download. You didn't actually purchase anything.

You should not be charged unless you started the Office 365 subscription.

You can verify that by following the steps in the support document you came from. If you don't see a a subscription for Office 365 following those steps, then you will not be charged for anything.

Your purchases section in the App Store doesn’t mean anything other than you have downloaded an app. If you swipe on the app, you can hide it from your purchased list.

All that should have done is allow you to download and install the Microsoft 365 applications. They are useless without purchasing a Microsoft 365 license via in-app purchases.