The Asus ROG Ally Z1 Extreme is a Windows 11 based gaming handheld PC. This is the higher end of the two Asus ROG Ally models with an AMD Zen 4 based Z1 Extreme CPU, 16GB of RAM, and a 512GB SSD.
Valve's handheld will set you back an additional $100 compared to Asus's right now (it's got a full $549 MSRP). Where usually this is considered the budget alternative to the best gaming handheld PC ...