Looking for help/advice - son’s PC

Hi everyone. Let me start by saying I know next to nothing about gaming PCs. I’m trying to help my son (10 yrs old) who is telling me his PC is slow - AVGPC Hellfire III Ryzen 5 5600X - 3050 GPU and monitor has 1080p resolution. He primarily plays Roblox. He’s asking for a graphics card for his birthday. I’m lost. Thank you for any recommendations. 😊