Two days ago on iPhone and iPad new emails have "Your network settings prevent content from loading privately" message. No system updates or settings changes. Wife's device experiencing the same issue.

Does this happen on Wi-Fi, cellular data, or both? If Wi-Fi, does it happen on all Wi-Fi networks, or just your home network?

If only on Wi-Fi, have you changed anything in your Wi-Fi router settings? Have you tried restarting your router?

Do you use VPN on these devices? If so, delete the VPN profile in Settings/General/VPN & Device Management/VPN. Don't just turn it off; delete the profile.