The current/latest Fedora_37 or Fedora_38 kernels (>6.2.y-200.fc37 or >6.2.y-300.fc38) are NOT recognized by "kexec" and as such will NOT boot up with petit-bootdisk or u-root-bootdisk. Users that downloaded the Fedora_38_Workstation for example, will find the that the freshly flashed Fedora_38_Workstation does NOT boot up using u-root-bootdisk or petit-bootdisk as per guidance on this post.
The good news is, you can use Fedora_36 kernels on Fedora_38 (tested on Fedora_38_Workstation). The two latest Fedora_36 kernels are 6.2.14-100.fc36 and 6.2.15-100.fc36 (Fedora no longer update/release Fedora 36 kernels anymore). With the Fedora_36 6.2.14-100.fc36 or 6.2.15-100.fc36 installed on Fedora_38_Workstation it will be able be boot up using petit-bootdisk or u-root-bootdisk.
/:-------------:\ jfl@fedora
:-------------------:: OS: Fedora
:-----------/shhOHbmp---:\ Kernel: aarch64 Linux 6.2.15-100.fc36.aarch64
/-----------omMMMNNNMMD ---: Uptime: 12m
:-----------sMMMMNMNMP. ---: Packages: 1858
:-----------:MMMdP------- ---\ Shell: bash 5.2.15
,------------:MMMd-------- ---: Resolution: No X Server
:------------:MMMd------- .---: DE: GNOME 44.2
:---- oNMMMMMMMMMNho .----: WM: Mutter
:-- .+shhhMMMmhhy++ .------/ WM Theme: Adwaita
:- -------:MMMd--------------: GTK Theme: Adwaita [GTK2/3]
:- --------/MMMd-------------; Icon Theme: Adwaita
:- ------/hMMMy------------: Font: Cantarell 11
:-- :dMNdhhdNMMNo------------; Disk: 16G / 56G (29%)
:---:sdNMMMMNds:------------: CPU: Unknown @ 6x 1.992GHz
:------:://:-------------:: GPU: Mali-G52 (Panfrost)
:---------------------:// RAM: 1246MiB / 3750MiB