I hope I'm not in the wrong community but I really wanted to get some opinions on that.
In short, it may be a it of an unpopular opinion, but I really hate the gaming aesthetics with all the RGB lights and glass and in general how modern 3rd party PC cases look like. On the other hand I really enjoy the look of a most of the recent Lenovo ThinkCentres and ThinkStations as well as Fujitsu's Esprimos. There is just something about this industrial matte black with red accents I can't resist.
What I would love to do is to take some cheap Lenovo Thinkcentre, slap a GPU in it and have a budget Linux gaming PC, but the problem is most of the parts in these office systems are proprietary. It seems that I can't easily upgrade the PSU to handle a proper GPU, nor can I swap the motherboard for a new one if I wanted to.
Does anyone have any idea on which models of ThinkCentres/Stations are easily upgradeable or of any cases that have this understated industrial office look to them? The only case I kinda like is the Fractal North, but I get really discouraged when I compare their prices to a fully equipped Lenovo office PC and it just doesn't look as good.
Also, I've looked into Lenovo Legion and HP Omen prebuilts, and while they're not as bad a 3rd party cases, I just don't like them as much as say a P520, which unfortunately comes with some awful proprietary motherboard supporting only Xeons from 2017.
Anyway, I'm sorry for the rant. I'd love to hear your opinions and suggestions.
If you are looking for some less garish designs for cases the Fractal Design North is one great looking option, and also some of the mini-itx form factor cases look really nice too, not too far off from some of the ones you mentioned.
That said, you absolutely can add a graphics card to some of the corporate machines, but some are much harder than others. I have not done one recently but honestly I would look for someone else's build and replicate it as exactly as possible. I have had weird issues with corporate gear before around connectors, weird pinouts, very limited PSUs, and strange limitations on the PCIe port supporting some cards but not others (HP and a generic network card crashing my system randomly). If you find that someone else has done that specific box with a specific card then you should be ok, but if you have to deviate try to make sure that you match closely what they had, such as whether the graphics card has extra power or is PCIe only or if they have to use one of the corporate style graphics cards because gaming cards won't work.