As mentioned by others, if your primary use case is storage/NAS with only one or two VMs, then for sure go with TrueNAS SCALE.
Where Proxmox wins is the easy backups for VMs/containers locally to disk, local NAS or remote NAS, easy management when you have a lot of VMs (I feel like there’s too much clicking through menus in the TN UI which gets annoying fast), more recent kernel and ability to use LXC.
I use both in my homelab and I keep TrueNAS as a NAS and Docker host via Jailmaker script (for services that benefit from direct/local file bind mounts) because I really dislike the way the TrueNAS Apps feature is handled.
In my experience, TN Apps are just not stable and seem to get randomly stuck ‘deploying’ for no good reason after being restarted or updated. Combine that with the general hostility of the forums and of TrueCharts, and so I decided to not have anything to do with the Apps feature. IX changed a few things to do with app storage that then forced TrueCharts to change how they do things, so there’s been a few occasions where the only solution has been to delete and recreate containers which pissed off a lot of users.
Jailmaker lets me use Docker Compose inside a systemd-nspawn container. It’s kind of funny how this nested containerisation method ended up being a hell of a lot more reliable than TN Apps. I don’t want this to sound like I’m ungrateful for the good things they’ve done for TN by making services easy to run, but their reading their posts, their behaviour and tone online just always makes me shake my head.