Simply reboot, as long as you have some console access (your screenshot shows IPMI viewer).
The proxmox boot menu should hold a setting to choose your previous kernel.
I am assuming this was working before...
ipmi does not show menu to select kernel.
I solved it by renaming the kernel 6.8.12-8-pve to 6.8.12-8-pve_ and forcing the grub to stop at the option screen.
System online again, thank you