Lawrence Systems did a good comparison between TrueNAS and Synology DSM. I do not have many complaints about his content except that I think he missed an inportant point…
as of June 2021 TrueNAS does have a backup solution that has a limited free level of subscription. The same can be said about the Synology email server licensing. You’ve missed a few things… First of all neither system regardless of the model has enough RAM or CPU cores to run large jails, VMs, or containers. Second TrueNAS is more of a operator or system admin based user interface where DSM is more like a GSuite clone. Emails, word processor, spreadsheets and so on. Sure they are both turnkey but they are meant for different audiences.
But everything else was pretty reasonable.