AnduinOS 2.0.2 installer cannot detect valid unallocated space or EFI System Partition in multi-Linux setup

Installer: anduinos-installer-beta 2.0.2-2+resolute
AnduinOS: 2.0.2
Installation mode: Live USB, booted in UEFI mode
Partition table: GPT

Summary

I am trying to install AnduinOS alongside four existing Linux installations on the same GPT disk:

CachyOS — Btrfs
Edubuntu — ext4
Zorin OS — ext4
Linux Mint — ext4

The system has a 4 GiB shared EFI System Partition, used by the existing CachyOS/Limine boot setup, plus approximately 291 GiB of completely unallocated space at the end of the disk.

I want to install AnduinOS into that unallocated space while leaving all four existing installations untouched.

The installer detects the disk and the unallocated space on the initial storage screen. However, after selecting:

Advanced — Keep existing systems

the installer displays:

Unallocated space: (None)
EFI System Partition: (None)

Both dropdown menus are greyed out and cannot be selected.

Therefore, I cannot proceed with the intended coexistence installation.

Installer behavior:

On the initial storage screen, the installer correctly displays the existing partitions and the approximately 291 GiB of unallocated space.

I select:

Advanced — Keep existing systems

On the subsequent Advanced: Install Alongside screen, however, I get:

Unallocated space: (None)
EFI System Partition: (None)

Both controls are disabled/greyed out.

There is no way to open either dropdown and manually select:

~291 GiB unallocated space

or:

/dev/sda1

as the EFI System Partition.
Verification from the AnduinOS Live environment

I verified the partition layout from the AnduinOS Live environment.
lsblk

lsblk -o NAME,SIZE,FSTYPE,FSVER,LABEL,PARTLABEL,PARTTYPE,MOUNTPOINTS

Output:

NAME SIZE FSTYPE FSVER LABEL PARTLABEL PARTTYPE MOUNTPOINTS
loop0 2.1G squashfs 4.0 /rofs
sda 476.9G
├─sda1 4G vfat FAT32 ESP-SHARED c12a7328-f81f-11d2-ba4b-00a0c93ec93b
├─sda2 50G btrfs Cachy-Root root 0fc63daf-8483-4772-8e79-3d69d8477de4
├─sda3 43.9G ext4 1.0 Edubuntu-Root 0fc63daf-8483-4772-8e79-3d69d8477de4
├─sda4 43.9G ext4 1.0 Zorin-Root 0fc63daf-8483-4772-8e79-3d69d8477de4
└─sda5 43.9G ext4 1.0 Mint-Root 0fc63daf-8483-4772-8e79-3d69d8477de4
sdb 298.1G
├─sdb1 298.1G exfat 1.0 Ventoy 0x7
└─sdb2 32M
sdc 0B
sdd 0B
sde 0B
sdf 0B
sr0 1024M
zram0 7.8G swap 1 [SWAP]

fdisk

sudo fdisk -l /dev/sda

Output:

Disk /dev/sda: 476.94 GiB, 512110190592 bytes, 1000215216 sectors
Disk model: INTENSO
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes
Disklabel type: gpt
Disk identifier: 23582D95-800B-41FA-B052-B381B4F12C71

Device Start End Sectors Size Type
/dev/sda1 4096 8392703 8388608 4G EFI System
/dev/sda2 8392704 113250303 104857600 50G Linux filesystem
/dev/sda3 113250304 205410303 92160000 43.9G Linux filesystem
/dev/sda4 205410304 297570303 92160000 43.9G Linux filesystem
/dev/sda5 297570304 389730303 92160000 43.9G Linux filesystem

Notably, fdisk explicitly identifies /dev/sda1 as: EFI System

and the disk uses: GPT

There are no partitions after /dev/sda5, leaving the remainder of the disk unallocated.
EFI partition

sudo blkid /dev/sda1

Output:

/dev/sda1: LABEL_FATBOOT="ESP-SHARED" LABEL="ESP-SHARED" UUID="E30B-2DAE" BLOCK_SIZE="512" TYPE="vfat" PARTUUID="071991eb-9375-4ece-b16a-c6706bac4767"

Boot mode

test -d /sys/firmware/efi && echo "UEFI mode" || echo "Legacy/BIOS mode"

Result:

UEFI mode

Therefore, the Live environment is definitely running in UEFI mode.

Installer version

The installed package is:

ii anduinos-installer-beta 2.0.2-2+resolute amd64

The Live environment otherwise reports AnduinOS packages at version 2.0.2-1+resolute.

The installer therefore appears to be:

AnduinOS native GTK4 installer — anduinos-installer-beta 2.0.2-2+resolute

Attachments

I have attached screenshots showing:

The initial disk-selection screen, where the ~291 GiB unallocated space is visible.
The Advanced — Keep existing systems selection.
The Advanced: Install Alongside screen where both Unallocated space and EFI System Partition are shown as (None) and the controls are disabled.

Question to the developers:

Is this disk layout supported by the AnduinOS 2.0.2 native installer?

If yes, could you please investigate why the installer rejects the existing unallocated space and EFI System Partition?

If no, is there currently a recommended way to install AnduinOS into existing unallocated space alongside multiple Linux distributions while preserving the existing shared ESP and bootloader setup?

Thank you for your time and afford!
PS: I hope its ok, that I used GPT for help in writing this.

Start by reproducing the issue in the AnduinOS native GTK4 installer, version 2.0.2-2+resolute, using the reported GPT disk layout and UEFI boot mode. Compare the initial storage screen with the Advanced: Install Alongside screen; done means valid unallocated space and the existing EFI System Partition are detected and selectable, or the supported-layout limitation is documented.