For many releases we have published daily ISOs on https://cdimage.ubuntu.com for the supported LTS releases. For example, the focal live server dailies are here:
These have always been aimed at helping the developers of Ubuntu prepare for the next LTS point release rather than for users to use – they have had the proposed pocket enabled, which is definitely not something you want on a system you’re using for real work!
However the reasons for having proposed enabled do not apply in the same way to the live server installer, so a few days ago we changed these to build without it. This means that they can now be used to install a generally useful system, one that comes with the latest version of subiquity built in and requires fewer package upgrades to bring it up to date.
Do note that this change is only for the live server installers, not any of the other installers or images.
The ISOs we produce daily obviously do not receive the same level of QA as the ISOs that get published on releases.ubuntu.com. But they still might be useful!
for the Ubuntu Server team