Tbh another archaic idea is that you need to transcode.
All you need is one of those sticks that plug into the hdmi of your tv and can run vlc. I use a chromecast. Vlc can play mkvs directly off samba shares. Done.
TBH the only reason anyone talks about transcoding is Synology's absolute dog-shit hardware options make it a problem. Most Intel CPUs and most AMD CPUs and many ARM CPUs and all the discrete GPUs are absolutely fine with munging video and audio codecs. They're just not well-represented in Synology's lineup.
Fundamentally I guess it feels like they have ground to a halt or even quietly retired the DSM line.
Let's look at your NAS for an example (it's actually worse for mine cause I always loved the Slims lmao).
DS1821 has no GPU transcoding because it uses the AMD Ryzen 1500B, what you've observed is this processor is just powerful enough to brute force some transcoding but it has no hardware transcoding:
DS1821 successor was recently revealed to be the DS1825. So if your NAS died in a few months, that would be your obvious choice for a replacement. They decided to continue using the AMD Ryzen 1500B, which is now seven years old. TBD if they bother releasing it this year. In a few months they could call it DS1826 instead.
Meanwhile DSM still lacks support for NVMe volumes, in fact there are still no NVMe-only models at all, you can't even install DSM to NVMe, they cut support for USB drives, they cut support for HEVC, and they almost never update docker and some of the other tools.
The hardware's going nowhere and the software's going backwards.
I would like to use ssds for running containers, this is a good point. The elderly cpu is more than adequate for my needs but as you say, an upgrade, ever, would be nice.
I guess I’ve avoided these issues by accepting that solid state storage in a NAS is still too expensive.
My ultimate would be the Synology with an Apple silicon heart. One can dream.
That said, the person you're replying to is right. Synology has mostly stopped supporting their apps, they've removed features in cost-cutting features (media codecs), hardware is now hopelessly outdated and both kernel and docker are completely out of date.
It feels like any technical leadership completely disappeared and now only bean counters who don't understand the product or their target market are making decisions.
It's hard to actually buy a computer that bad these days, although Synology still makes it easy lol.