When installing ubuntu server, I always want and recommend RAID-1 since hard drive failure is one of the most frequent problems with servers. The server installer supports this but doesn't end up with a fully redundant setup, because it doesn't (by default) create a second boot partition on the 2nd hard drive, so if the first drive dies your data will be safe but the server won't be bootable. This can be worked around without too much problem, but should really be handled in the installer so that people who don't think about this issue don't end up with a non-bootable system.
https://calvin.me/install-ubuntu-18.04-on-raid1 has instructions on accomplishing the goal manually; I would expect implementation within the installer to have a similar outcome
https:/
My suggestion with this bug report is that such should be the default behavior when setting up a system with RAID-1 (which in turn perhaps should be the default when you're installing on a system with two similarly-sized hard drives...).
In the mean time I'll look again for where subiquity supported multiple ESPs, or if someone knows how that is done they might point me and others in the right direction...