Digital Foundry did an incredible job showing how the Deck is a PS4-powered handheld console, running the same game with the same graphical settings, at its native resolution, with the same/better framerate. :
Fallout 4 - PS5 vs PS4 Frame-Rate Test Gameplay - YouTube
Fallout 4 Runs at a Boosted Frame Rate of 60 FPS on Xbox Series S
Fallout 4: Far Harbor re-released on PS4 to fix performance issues - Polygon
Fallout 4: PS4 Pro Patch Analysis + Boost Mode Frame-Rate Tests | Digital Foundry
Fallout 4 PS4 - Patch 1.8 (1.08) gameplay update / frame rate test (No mods, bethesda, rly?) - YouTube
Fallout 4 Far Harbor DLC: PS4 vs Xbox One Gameplay Frame-Rate Test - YouTube
True 4K or Smoother FPS – Fallout 4 Xbox One X vs PS4 Pro Comparison
Bethesda Re-releases Fallout 4: Far Harbor On PS4 To Solve Frame-Rate Issues
The Outer Worlds PS4/Pro vs Xbox One/X Frame Rate Comparison By VgTech | NeoGAF
PS5 now runs Skyrim at 60 fps — here's how to enable it | Tom's Guide
Performance Analysis: Fallout 4 PS4 & Xbox One Has "Issues Holding 30fps," Smoother Experience Is on PS4
Fallout 4 mod improves frame rate by sacrificing textures | VG247