Under most circumstances, this is caused by enabling Apple's "Private Relay" functionality. For more information on that feature, you can review Apple's documentation here: https://support.apple.com/en-us/102602
This will have no negative impact on your Loupe account, and you will still receive correspondence from Loupe regularly. If you wish to review how to toggle this function, Apple provides information on that process here: https://support.apple.com/guide/icloud/set-up-icloud-private-relay-mm7dc25cb68f/icloud
Note that if this function is enabled or disabled after your Loupe account has been created, you will be prompted to create a new Loupe account when you sign in, as on our end we would see a change in the associated email address.