The iso files of Ubuntu Desktop 23.10 and Ubuntu Budgie 23.10 are getting withdrawn, then fixed and released
Those iso files are being updated to resolve a malicious translation incident. If I understand correctly, it affects [only] the iso files with the new installer. It means that the corresponding 'legacy iso files' with the old Ubiquity installer are good and still available at
cdimage.ubuntu.com/ubuntu/releases/23.10/release/
and
cdimage.ubuntu.com/ubuntu-budgie/releases/mantic/release/
where you also find the sha256sums.
There are more details at this link to Ubuntu Discourse.
The other 23.10 iso files and image files are not affected and still available.