Very difficult to get a truly silent build that's still capable somewhat. Maybe something like this? Only added a decent aftermarket cooler as the stock Ryzen one is noisy...
Case is pretty good. If it's still audible that he can't handle it, get it in a cupboard with some ventilation if possible?
I was gonna go with a 500GB SSD, but thought if he's tearing through games a lot, 1TB should hopefully keep him content to have a fair few installed to hop between.
May have to look elsewhere for stock on certain parts, namely the CPU and Mobo.
My basket at Overclockers UK:
Case is pretty good. If it's still audible that he can't handle it, get it in a cupboard with some ventilation if possible?
I was gonna go with a 500GB SSD, but thought if he's tearing through games a lot, 1TB should hopefully keep him content to have a fair few installed to hop between.

May have to look elsewhere for stock on certain parts, namely the CPU and Mobo.
My basket at Overclockers UK:
- 1 x AMD Ryzen 3 3100 Quad Core 3.9GHz (Socket AM4) Processor - Retail= £99.95
- 1 x Gigabyte A520M DS3H (Socket AM4) DDR4 mATX Motherboard= £67.99
- 1 x Team Group Vulcan Z T-Force 16GB (2x8GB) DDR4 PC4-25600C16 3200MHz Dual Channel Kit - Grey= £49.99
- 1 x Asus GeForce GTX 1650 SUPER TUF OC 4096MB GDDR6 PCI-Express Graphics Card= £158.99
- 1 x WD Blue 3D NAND 1TB 2.5" SATA 6Gbps Solid State Drive (WDS100T2B0A)= £94.99
- 1 x Alpenfohn Brocken 3 CPU Cooler - 140mm= £42.95
- 1 x CoolerMaster Silencio S400 Silent Micro ATX Case - Black= £79.99
- 1 x Corsair CX-M Series CX550M 550W 80 Plus Bronze Semi Modular Power Supply (CP-9020102-UK)= £67.99