Plex in highest quality via Samsung 82 inch TV, old Microsoft Surface 5 and several Android tablets or mobiles absolutely smoothly, even 4k. CPU of the 923+ not over 30% in each case

Initially, I streamed to Apple TV with the Synology app Video Station. For months now, I've been having much more fun streaming video data (mkv, mpg, mp4, iso) with Infuse. Above all, it is the first app that provides me with the ISO files without any problems. The whole thing runs over wifi with my 4-year-old Orbi.

Streaming per se does not require a GPU.
A GPU is helpful when transcoding takes place at the same time. That is, if your client does not understand the codec used to store the data.

Synology DS923+ is already the second storage station from Synology that I have purchased. The new device is currently in reserve because the first station (DS920+) still has storage capacity available. I need the devices exclusively as storage and production devices in combination with an iMac (Retina 5K, 27-inch, 2019) and the Final Cut Pro programme for film productions. This combination works flawlessly and quickly. Playback of even high-resolution films is absolutely smooth.