I can confirm, this installer, on a blank hard disk, booted in legacy mode, does indeed use GPT partitioning and Bios-Boot-Partition, even if the disk is under 2^32 sectors (i.e. less than 2TB with normal 512byte logical sectors on the interface).
This is problematic, as some legacy non-EFI-bootable systems (I noticed on "Intel Desktop Board" systems I think) -- require a 'bootable' partition in the MBR, not just the 55AA on last 2 bytes. It may be they could put in hybrid-mbr-entry for the bios-boot-partition to be listed in the MBR table (and marked 'bootable') as well as the GPT table, or otherwise put the '80' boot flag for the last MBR entry (not really in use). You must not set the GPT protective container entry in MBR as bootable, as some EFI/OS will not consider this a valid GPT disk.
The 'simplest' workaround for those affected, is to manually partition the disk as MBR, even if it still has an EFI-system-partition type 0xEF and a linux EXT4 partition to boot from.
This is the same situation as the 3-way-bootable linuxmint install-iso, MBR partitioning with active partition, GRUB on MBR, ESP 0xEF, and DVD no-emulation-bootable as well.
This will need thinking about for release-notes, or so.
(less important now) Clem: better solution confirmed for memtest, install 'pcmemtest' 22.04 package and those files for your boot images from beta:-
Use "linux /boot/pcmemtest.bin" for non-UEFI memtest [I find this works on more older systems than memtest86+]
Use "linuxefi /boot/pcmemtestx64.efi" for UEFI memtest [WORKS in common 64bit EFI booting!]
cinnamon-settings sound module test window broken (shows all possible speakers instead of what you have).
Direct launch of accessibility settings from menu broken (fixed in cinnamon git)
I can confirm this installer (even booted in legacy mode) does indeed create ESP [EFI system partition] on existing Legacy multi-boots, but nonetheless works both for legacy-booting and for EFI-booting . I think this is overall a positive change providing forward/backward compatibility, subject to caveat below.
The release notes may want to explain this can cause some systems to EFI-boot when they wouldn't before, and potentially prevent multi-booting into a non-EFI-capable legacy OS [e.g. netbook I have here always prefers ESP over any legacy booting unless Esc-key tapped for boot menu every time, no matter what you do in BIOS-settings], even if you change the partition-type from 0xEF to 0xC ... it still finds and EFI-boots it!.
#045: repository keys: Not a show stopper but just wanted to point out the warning message. "Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8))." Everything else was fine.