This blog by RFSysadmin saved my #Proxmox install after the upgrade from 8 to 9. It seems like the #EFI boot sequence got blasted in the update (i thought, i was careful) and proxmox 9 rebooted into the BIOS.
Long story short: Boot into the rescue enviroment (login is your root login)
fix the EFI settings like mentioned in the blog
Reboot and keep enjoying that #homelab
Step by step guide here https://blog.rfsysadmin.com/proxmox/how-i-fixed-my-proxmox-server-after-upgrading-to-proxmox-9-stuck-booting-into-bios
👉 Dualboot Windows-Linux EFI avec rEFInd Boot Manager ✔

👉 Dualboot Linux EFI avec rEFInd Boot Manager ✔

CSMWrap arriva come soluzione elegante per far partire sistemi BIOS legacy su macchine moderne prive di CSM. Un’app EFI che integra SeaBIOS e riporta in vita vecchi OS su hardware UEFI‑only. #CSMWrap #UEFI #Linux #OpenSource #EFI
After way too many attempts, I finally got a custom GRUB2 EFI bootloader built with Buildroot showing a splash image at boot on real hardware 🎉
The secret? insmod gfxterm_background + font in the right path.
Simple in theory, painful in practice 🤕
Explainer: Mac firmware version numbering
https://fed.brid.gy/r/https://eclecticlight.co/2026/03/07/explainer-mac-firmware-version-numbering/