CAUTION: This manipulates system files! USAGE AT OWN RISK!
Modify your desired logo to „logo.png“ (size = 175px X 30px) and save it in, either /root or any folder you want to use,
then login as root to your Proxmox VE via SSH:
#backup original cp /usr/share/pve-manager/images/proxmox_logo.png /usr/share/pve-manager/images/proxmox_logo.png.bak; #copy custom cp </path/>logo.png /usr/share/pve-manager/images/proxmox_logo.png;
Enjoy!