I'm having a little trouble finding an answer to this on Google. Hoping someone can help me out.
I have the "Lenovo ideacentre 720-18asu" tower, Model Number is "90H10004US". It has the Radeon RX 560 (4 GB) graphics card, and according to the Command Prompt, the motherboard is a "Lenovo 3100". I'm just curious if anyone can tell me what the best graphics card is that the aforementioned motherboard can handle?
The motherboard is not the problem. It can accept any PCIe x 16 graphics card, which is every new card on the market.
Your issues are:
Power supply - The 400W one in there's really minimal for an RX 560 and Ryzen 7. You should be upgrading the power supply, but Lenovo still uses their proprietary 10 pin connector instead of 24 pin.
You need THIS adaptor, and probably should buy it now anyway in case you ever need a new power supply.
With an upgraded power supply, then you still have to consider the physical fit of a card.
You will have to open the system and measure the length, or rebuild into a new computer case for long cards and better air flow. You could also get an interference in card height with the cage support Lenovo used.
I can see in the pictures how crowded it is in the system.
It should be a standard uATX motherboard and only real issue of a new case is whether a wireless card has an antenna connected to the case and may need that fix. The RX560 they used is a short length.
Your country and money available for a new card is key, because cryptocurrency mining has pushed up the prices of new high end cards.
You really can't upgrade from RX 560 without a new power supply, and that has to fit in length as a check.
They used a thin laptop-type DVDRW also.
If not skilled at it, you should ask around for who knows how to re-build a PC.
Although they call it upgradable, almost every branded PC is a nuisance.
You should name your country, budget, and whether you want to rebuild it.
To keep the thin dvdrw you would need an adapter of some sort or a faceplate in making it horizontal.
You lose the memory card reader in a new case unless you buy one.
pcpartpicker.com helps with shopping.
Your motherboard is not a concern.
Power supply and computer case are the issues, and cost.
A gpu needs watts - power. It gets this from two places the SLOT and the external power cables(that a PSU must provide). Typically a SLOT can only manage about 60 watts but up to 75 at a push. Therefore most pc makers which supply Low End PSU's with their pc's usually offer GPU upgrades of around 45 to 60 watts. This is because their low power PSU won't have the additional power cables(because the low power PSU isn't able to provide any extra so its a waste of time adding the cabling). So basically your PSU decides what GPU you can fit. The specs of an RX560 are 60-80 watts and a recommended min PSU watts of 450. So you are probably maxxed out already.