Optiplex build FTW?

Hey there :>

I'm planning on getting my nephew a gaming PC instead of a console. I'm thinking about getting a used SFF Dell Optiplex with an 8th gen i5 (found a couple going for around 500 AED, ~135 USD) and throwing in an RX 6400.

It's going to sit in the living room for now (thus, SFF). He's mostly gonna be playing easy to run games like minecraft, roblox, platforms, racing games, etc., so it should be more than enough for his needs.

Can anything beat the price/performance in this budget? Anything I should keep in mind or be aware of?