I’ve got Yahoo mail and I have no problems at all. I did the upgrade within hours of it coming out.
I would suggest first deleting your Yahoo account “on the Apple device” - then setting it back up again.
If that doesn’t work, then I would do a full and total backup on iTunes, then when you’re assured the backup is there and is safe — then RESET your device to original factory condition, and restart the device and use your backup to bring it back to your previous state.
If that doesn’t work, then I would head on down to the Genius Bar at the Apple Store and have them look into your device.
Did first stuff. Ready to try iTunes but is it safe and is your dada safe? Lot of work?
Can we just
Backup data to a PC instead of sending it out to the internet?