My workaround was to
1) manually create, format and open the physical volume for encryption
2) launch Ubiquity, and in Manual disk layout choose the /dev/mapper/sdaX_crypt volume as / (root) without formatting
3) complete the installation but choose Continue Testing
4) chroot into target, create crypttab and check fstab, update-initramfs
Main issue is duplicate of https:/ /bugs.launchpad .net/bugs/ 1510731 /bugs.launchpad .net/bugs/ 1510730
Secondary issue is a duplicate of https:/
My workaround was to sdaX_crypt volume as / (root) without formatting
1) manually create, format and open the physical volume for encryption
2) launch Ubiquity, and in Manual disk layout choose the /dev/mapper/
3) complete the installation but choose Continue Testing
4) chroot into target, create crypttab and check fstab, update-initramfs
for step-by-step instructions see https:/ /github. com/artmg/ lubuild/ blob/master/ help/configure/ LxQt-Kubuntu- Ubiqity- manual- encryption- bug.md