Thanks for the suggestion. I looked into the P series cards a bit and here is what I found:

The NVIDIA 50-series Blackwell cards require the use of the new open GPU kernel module, but several of NVIDIA’s older generations of GPUs - including the Maxwell, Pascal, and Volta generations - lack the GPU System Processor (GSP) module on their silicon in order to leverage the open kernel module, and thus will no longer function. This includes the GTX 700-series, 900-GTX series, GTX 10-series, the Quadro M-series and P-series, and Tesla M-series and P-series cards.

Looks like the 16xx is the lowest cards supported by TrueNAS without extra work. There’s a few used 1660s in my area for ~$100. I might give that a try. If it doesn’t work out, I won’t be despairing for weeks about a $100 card, and if it does work, I’ll replace one of the 1080s with a 1660 for TrueNAS to use as an apps card and leave the other 1080 to pass through to the VM for Home Assistant.