F5 VE on Proxmox

Yes, I got it working, I had the exact same problem as you. I used a converted vmdk image, but that behaves exactly like the qcow2 image so I dont think that has anything to do with it. In short, I activated the license via CLI instead of GUI. Here is the complete procedure:

1. Create a VM, with any disk. It will be deleted later anyway. I used 16 Gb RAM, 2 sockets 4 cores CPU, Machine: i440fx, SCSI-controller: VirtIO SCSI, NICs: VirtIO
2. Detach the disk from the VM and delete it.
3. Download the qcow2 image from F5
4. SCP it to Proxmox
5. unzip it. apt install unzip if needed.
6. Attach the qcow2 file to the VM, and move it to designated storage: qm importdisk <vm-id> BIGIP15.1.x.y.z.qcow2 VM-storage
7. Doubleclick on the now unused disk image in the VM hardware settings. Add it.
8. Boot VM. Bring up a console. It shows nothing of the boot process except the GRUB menu, but the login prompt eventually comes.
9. Login. Set root password.
10. mcpd reboots in a loop. Kill it: tmsh stop sys service mcpd
11. mkdir /shared/.snapshots_d
12. tmsh start sys service mcpd
13. Wait a while. Then run config and set mgmt IP.
14. Login to GUI. You are forced to update GUI password.
15. Go though license activation procedure.
16. Dont know if it matters, but I chose offline activation. It "succeded" but when provisioning modules in the next step AVR is the only licensed module.
17. Leave it there and bring up a console.
18. Active license via CLI: tmsh install sys license registration-key <regkey>
19. Magic happens
20. Complete the setup in the GUI.

I used BIGIP 15.1 on Proxmox 6.1. Maybe license activation in the CLI right away works, but the above procedure is exactly how I did it. As far as I can tell, F5 states that VE should run under KVM, this seems to be a Proxmox-specific thing. I have run multiple BIGIP under KVM earlier (like GNS3 server) and never had this issues.

I have not run my unit very long so I have no idea how it will behave over time... but hopefully this helps someone.

UPDATE: The VM behaved weird in several ways. It seems fine in the GUI but there are issues. sshd would not start via systemd, and several services failed to start, big3d rebooted in a loop after a while. Some of it seems related to SELinux, sshd did start when SELinux was set to permissive ("setenforce 0"). sshd also started if you started it manually. Other services like network and f5-label did however not start. Never found out why. However a better workaround for me was booting 13.1, which start without issues. Then upgrade to the version you want. I got no errors at all. The exact version I used was BIGIP-13.1.3-0.0.6.ALL.qcow2.zip, then jumped to BIGIP-14.1.2.3-0.0.5 and then BIGIP-15.1.0.1-0.0.4 and they all worked just fine.