Problem as explained in description.
I reported it as a zypper problem, so this issue will probably be closed as
invalid: https://github.com/openSUSE/zypper/issues/564

    OS: openSUSE Tumbleweed
    Bootloader: systemd boot
    Other info: encrypted filesystem
    Does this always happened? At least I can confirm it for the last two
kernel updates.
    Which files are the ones I'm reporting as not having been deleted as
expected? They're under /boot/efi/bad01a2647cb4fef8827293b9d389245 (obviously
the last directory has some random string related to systemd boot). There's a
kernel directory for each installed version there, containing the kernel itself
and at least one initrd (more if dracut has been called several times).
    Why am I reporting this? The default size for /boot/efi defaults to half a
GB, which seems to be enough... Well, I'm definitely going to double that in my
next installation, but even with the default 2 kernels, this is easy to fill if
calling dracut for whatever reasons (and sometimes, scripts are the ones
calling it). If one of the kernels to be purged is not actually purged there,
the partition gets filled very easily.

I'm attaching some output to illustrate it. Let me know if you need anything
else. Please also let me know if this is not zypper purge-kernels's fault (and
if possible, point me to where to report this).

mordor:~ # rpm -qa | grep -i kernel-default
kernel-default-6.10.3-1.1.x86_64
kernel-default-6.10.4-1.1.x86_64

mordor:~ # uname -a
Linux mordor.arkayate.org 6.10.4-1-default #1 SMP PREEMPT_DYNAMIC Mon Aug 12
05:49:20 UTC 2024 (0363a35) x86_64 x86_64 x86_64 GNU/Linux

mordor:~ # ls -l /boot/efi/bad01a2647cb4fef8827293b9d389245/
total 12
drwxr-x--- 2 root root 4096 Aug 16 22:55 6.10.2-1-default
drwxr-x--- 2 root root 4096 Aug 16 22:55 6.10.3-1-default
drwxr-x--- 2 root root 4096 Aug 16 22:55 6.10.4-1-default

mordor:~ # du -sh /boot/efi/bad01a2647cb4fef8827293b9d389245/*
175M    /boot/efi/bad01a2647cb4fef8827293b9d389245/6.10.2-1-default
95M     /boot/efi/bad01a2647cb4fef8827293b9d389245/6.10.3-1-default
175M    /boot/efi/bad01a2647cb4fef8827293b9d389245/6.10.4-1-default

mordor:~ # df -h /boot/efi/
Filesystem      Size  Used Avail Use% Mounted on
/dev/nvme0n1p1  511M  449M   63M  88% /boot/efi

mordor:~ # zypper purge-kernels -D
Reading installed packages...

Preparing to purge obsolete kernels...
Configuration: latest,latest-1,running
Running kernel release: 6.10.4-1-default
Running kernel arch: x86_64

Resolving package dependencies...
Nothing to do.

In the output above, the directory
/boot/efi/bad01a2647cb4fef8827293b9d389245/6.10.2-1-default should get deleted
(I believe that by zypper purge-kernels, but not 100% sure).

P.S.: Completely unrelated, but I'm happy to have seen that my FDE encryption
with TPM chip as decryption key now survives kernel updates, this was also
broken and got fixed recently, even before I could report this.