Amazon.com: ADT-LINK M.2 Key M NVMe External Graphics Card Stand Bracket with PCIe3.0 X4 to Thunderbolt 3 Riser Cable PCI-Express External Adapter Cable EGPU Adapter 25cm 50cm 32Gbs for ITX STX NUC (
Upgraded TH3P4G3 Thunderbolt-compatible GPU Video Card Dock Laptop to External Graphic Card for Macbook Notebook PD 60W 40Gbps _ - AliExpress Mobile
If the Steam Deck actually has an open x4 PCIe 3.0 slot you could have an eGPU solution while docked. That many 3.0 lanes is plenty enough bandwidth for something like an