The d-i based installer is still available and supported for bionic.
It's all documented here:
On Mon, Jun 4, 2018 at 10:48 AM, Phillip Susi <firstname.lastname@example.org> wrote:
Apparently d-i has been replaced with something called "subiquity". It
does not support raid or LVM; you know, things you typically install on
a server. It also ignores existing partitions on the drive and forces
you to blank the drive and start from scratch. Who thought this was
ready for production?
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