I am using a nearly identical iMac i7 since 2019, and it's still just fine for me. I got it as an Apple refurb, it is a BTO item they had. I use external SATA SSDs on USB3 for Final Cut ProX video editing or Reaper audio edits and it's fine for me, didn't bother with Thunderbolt due to added cost. I did up the RAM to 40GB right away. That said, Apple Silicon is the future for sure, and I recently bought a refurbed Macbook Air M2, with the thought of having a small portable and maybe accessorizing it for desktop use. It's a bit unsettling how fast they change M processors, however the iMac is still my daily driver. Here are some +/- thoughts;
+ (plusses)
..seems cheap, if working OK. Talk them down, offer $200!
..assuming 27 inch, the 5k screen is very good; cannot be used as a standalone screen
..I don't have a problem with speed for FCP videos, Reaper, or Affinity Photo, but I might be happier with newer speeds. Just use all SSDs and Thunderbolt or USB3.x storage.
..very quiet, unless pushed hard and fan activates
..built-in speakers are surprisingly decent
- (minuses)
..it's a 2017 computer, so without the latest speeds for Thunderbolt/USB, graphics, etc.
..old enough that aging electronic components may be a consideration; it could die tomorrow
..500GB SSD is small now, and may be due for upgrade due to size & wear. PITA to open up the computer and install a larger SSD, which is a special Apple size. You could run everything from an external Thunderbolt SSD.
..When Apple drops security support for the last MacOS it runs, you have to decide to risk keeping it online, or disconnect it and run it iso. Similar for apps, you may have to run older apps.
..camera is 720p and not great, so Zoom calls are subpar.