All my memos have disappeared, where are they?

First make sure you are looking in the right app. Each version of Audio Memos (SE, standard and pro) is a different app. Each app will contain its own list of memos (except if you activated the "Use iCloud" setting in multiple apps).

If you recently updated your version of iOS and have activated the "Use iCloud" setting, you might need to sign in iCloud once again (you can do that in the iCloud section of the Settings app).

If you recently synced your device with your computer and the syncing process deleted Audio Memos after displaying a confirmation message, then the syncing process deleted all your memos. See the answer to "How can I recover a deleted memo?".