Proxmox Host /boot is  98% Full 

how the Disk is used? # df -T -h


look with "pveversion -v" and still keep the latest and the running kernel.

cd /boot
/boot# ls -lha


Seems you have a lot of kernels installed.
You can list those packages with:  
# dpkg -l |grep pve-kernel


And you can remove them with:  
# dpkg --remove <pgname>