Startup Disk Creator doesn't create an extra `writable` partition as it used to

Something strange.

2 days ago, I used Startup Disk Creator (SDC) to prepare a USB Drive for an Ubuntu 24.04.1 install (on my 22.04). The USB stick is a USB-C (USB 3) 64GB drive.

That created the usual bootable Ubuntu install partition + another ext4 partition named writable using the remaining space, that's convenient to move data using that extra partition.

Today I used again SDC on a USB-A (USB 3) 32 GB drive (still on my 22.04). But this time it didn't use the remaining space (~23GB) to create a writable partition. The 23 GB is lost.

So I thought it's maybe because 32 GB is too "small", or maybe because it's USB-A...

To be sure, I erased the initial 64 GB USB-C drive (dd...) and run SDC again ...

This time it didn't create the writable partition anymore...

Are there other criteria to consider (or it's random??)

-- edit --

1. I realize that maybe (don't remember) I only mounted the USB drive on the newly installed 24.04.1 system (thanks to that drive), and 24.04 may show a partition that 22.04 doesn't?

2. Or, another possibility, the writable partition is created on the USB drive during the install?

Can someone please confirm 1. or 2. (or ...)

Rather than using Startup Disk Creator, I did this:

• Download the ISO.

• Copy it to the USB:

  $ dd if=ubuntu-26.04-desktop-amd64.iso of=/dev/sdb bs=4M status=progress oflag=sync
  

• Create a new partition:

  $ fdisk /dev/sdb
  n
  p
  default start
  default end
  w
  

• Name and label the partition:

  $ gparted
  Add partition name Writable.
  Add partition label writable.
  

It worked (I could write files to the sdb4 partition), but I don't guarantee I did everything the best way.

I then took the USB to another Ubuntu system:

• Only the boot ISO auto-mounted. (Perhaps I missed a step.)

• After the new partition was mounted manually, I could create new files in it.

  $ mount /dev/sdb4 /mnt
  
  $ ls -l /mnt
  total 20
  drwxr-xr-x 4 root root  4096 Aug  1 22:44 install-logs-2026-08-02.0
  drwx------ 2 root root 16384 Aug  1 22:14 lost+found
  
  $ ls -l /mnt/install-logs-2026-08-02.0/
  total 8
  drwxr-xr-x  2 root root       4096 Aug  1 22:45 crash
  drwxrwxr-x 10 root messagebus 4096 Aug  1 22:47 log
  
  $ ls -l /mnt/install-logs-2026-08-02.0/log
  total 996
  -rw-r-----  1 root       adm             0 Aug  1 22:45 apport.log
  -rw-r-----  1 dhcpcd     adm          7459 Aug  1 22:58 auth.log
  -rw-------  1 root       root        32684 Aug  1 22:47 boot.log
  -rw-r--r--  1 root       root         1588 Aug  1 22:44 casper.log
  drwxr-x---  2 gnome-remote-desktop gnome-remote-desktop   4096 Aug  1 22:45 chrony
  -rw-r-----  1 dhcpcd     adm         86771 Aug  1 22:48 cloud-init.log
  -rw-r--r--  1 root       root         3267 Aug  1 22:48 cloud-init-output.log
  drwxr-x---  2 root       lp           4096 Aug  1 22:46 cups
  -rw-r-----  1 root       adm         95109 Aug  1 22:46 dmesg
  drwx--x--x  2 root       975          4096 Aug  1 22:47 gdm3
  -rw-r--r--  1 root       root         1666 Aug  1 22:45 gpu-manager.log
  drwxrwx---  3 root       adm          4096 Aug  1 22:49 installer
  drwxr-sr-x+ 3 root       systemd-journal        4096 Aug  1 22:44 journal
  -rw-r-----  1 dhcpcd     adm        130570 Aug  1 22:58 kern.log
  drwx------  2 root       root         4096 Aug  1 22:45 private
  lrwxrwxrwx  1 root       root           39 Aug  1 22:45 README -> ../../usr/share/doc/systemd/README.logs
  -rw-r-----  1 dhcpcd     adm        611683 Aug  1 22:58 syslog
  drwxr-xr-x  2 root       root         4096 Aug  1 22:45 sysstat
  drwxr-xr-x  2 root       root         4096 Aug  1 22:46 unattended-upgrades