Never new exactly what a matx was but after googling matx cases and quickly googling am4 matx motherboards my options are endless on what spec components I can have, graphic cards options is a lot better and maybe it will work out a little cheaper than buying and building a itx gaming system and being limited on what itx mini graphic cards there are...
So in order of size itx is the smallest, matx then atx being the largest..
Good little learning curve and great advice and now my options has broaden ty
ITX gives the broadest possible range of case options; the variation in this market is huge (particularly when you add in smaller micro ATX cases, which provide a great alternative to the larger ITX ones). The main downside is you lose expansion slots and case features (manly fan and SATA ports), motherboard layouts can be cramped, and ITX can get expensive at the small end of the scale.
Unless you go really small and specialist, you can ignore ITX GPUs. By the time you get to a case that requires one, you're at a quarter of the size of a small Micro ATX case anyway, so not really comparable.
The NZXT H200 is one of the larger ITX-only cases, coming in at 27 liters. You get support for GPUs up to 325mm long, and ATX PSUs up to 311mm. In terms of cooling, it will fit tower coolers up to 165mm tall, a 240mm radiator in the front (and a 120mm in the rear) and there's enough space to fit a simple custom water cooling loop. Basically, you could take a typical ATX PC and transplant it in to this case, only swapping out the motherboard and (maybe) the CPU cooler (assuming a water cooler with a radiator larger than 240mm).
As a similar alternative, the Inwin 301 and Bitfenix Prodigy are a similar size with support for ITX and Micro ATX. Aside from Micro ATX support, these cases are quite similar to ITX cases at this size (the Prodigy even started life as an ITX case).
At the other end of the (gaming) scale, the Dancase A4 is only 7.2 liters in size. GPU support drops to 295mm (which is still more than enough space for a full size card). You lose support for ATX power supplies (swapping to SFX or SFX-L instead). Cooling options change completely; tower coolers and custom WC loops are pretty much out. In their place, there's a whole market of low profile CPU coolers designed to provide the best possible performance in a small case like this. These small cases need a bit of money throwing at them, as you'll need a new PSU, new cooling (in most cases), possibly a smaller GPU (if you had a particularly long one previously), and storage will need to be swapped to SSD/M.2. The main caveat with the Dan, is that cooling performance isn't amazing (hence the Vega warning; people have done it, but unless you already own one or are a really staunch AMD fan, an NVIDIA card would be the smarter pick).
Between these cases there's a sea of choices to fit just about any set-up. And if GPU requirements are more modest, and funds a bit more flexible, you can go quite a bit smaller than the Dancase.