

It will be controlled by Truenas not Proxmox. Truenas can add swap space to each drive automatically: https://www.ixsystems.com/documentation/truenas/11.3-U2.2/storage.html
But you probably already have existing drives so that doesn’t help. This might though: https://wiki.debian.org/Swap
But be aware that Truenas is design to be an appliance and doesn’t really want you tinkering under the hood. So you may have to manually add the SWAP after each boot of TN.
I would guess the best long term fix would be moving services out of the TN VM and into a different VM.
I am no expert, so grains of salt and such. But my assumption is that it’s a marketing expense. They get a lot of people familiar with cloud flare services and some of them later need a professional level solution. So people use what they are already familiar with. This is the same reason why tech companies provide hardware/software to schools for cheap/free.