The migration process involves knowing FreeBSD and jails and/or jail utilities. If you are familiar with it great, else further reading is required(documentations)..

In short, you want to be running FreeBSD along-side Proxmox..then install FreeBSD and set up networking, do a binary upgrade of FreeBSD to the latest patch release..

After that upgrade pkg to the latest as well. Then with the base and pkg upgraded, you can proceed to set up your first jail. Either using jail.conf(5) or BastilleBSD, the choice is up to you..structure is important so some planning is required..

Now comes the tedious part, installing and configuring all the required packages to mirror what you already have on Proxmox..copying all the configurations over, editing and testing them one by one to make sure they all work..

Good luck 🙂