Deleting voice memos from Icloud deleted them completely

There is nothing to fix. Syncing with iCloud means that any file changes on one device are replicated on all devices and in iCloud. When you deleted the files in iCloud, you therefore deleted files everywhere.

As you indicated. Your memos were in icloud which means that the memos synced. If you delete, it deletes everywhere. It’s unusual for settings to change but I suspect you may have conflates iCloud sync with your backup settings.

It's absurd that deleting files from the cloud also deletes them from the actual device. That kind of defeats much of the purpose of having a cloud backup

You're conflating iCloud sync with storing your backup in iCloud.

Unser Settings > Apple Account > icloud

If voice memos is enabled, it is syncing using iCloud to all of your devices. This is not a backup per se as anything that you do on device or at iCloud.comm will reflect on all devices. Hence the sync. If off, then voice memos are not synced. Items not synced are stored in your device backup.

Your device backup (if enabled) includes any items not already synced to iCloud. Essentially your device uses iCloud to store a backup.

Look at settings> Apple Account device backup or iCloud backup. If enabled, your device is making a backup and saving it to iCloud. You cannot browse or see what is contained in the backup. It can only be used to restore a device by first resetting it to factory settings.

If you did noR make a new backup after turning on iCloud sync, your memos may still be in your device backup. You can disable iCloud sync for memos, reset the device and set it up using your backup.