I have this specs:

Ryzen 5 5600

GTX 1050 Ti 4GB

16GM RAM DDR4 3600GHz

SSD SATA3 500Mb/s

and with this actions i have 60-80fps in game.

Texture Quality - Ultra or High;
Anisotropic Filtering - X16;

All other Setting set on Low or Off;

If you have RTX videocard, enable DLSS. If not, enable TAA.

Graphics API - Vulkan(test it, maybe Dx12 better for you).

You can try Lossless Scaling app in steam,
with this settings:
and play in 1280x720

Go to Nvidia Control Panel -> Manage 3D Settings -> Program Settings -> "Select program to customize:" add RDR2.exe -> "Specify the settings for this program:" -> Image Scaling set On and Sharpening 40-80%.

In game set resolution from 1280x720 to 1600x900, and Off VSYNC.

I use 1280x720, NIS 100% Sharpening, FSR 2(DLSS mod) Perfomance with 100% Sharpening.
This feature can work bad for you, test it.

DLSS unlocker(only if you have AMD, Intel or Nvidia GTX videocard)
DLSS to FidelityFX Super Resolution 2.1.2[www.nexusmods.com]

ASI Loader ScriptHookRDR2 V2[www.nexusmods.com]

Hardware-Accelerated GPU
Go to Windows Settings -> Display -> Graphics
Set On for "Optimizations for Windowed Games" and
"Hardware-Accelerated GPU Scheduling".

GPU Preference
"Add Desktop App" and select RDR2.exe,
set High Perfomance.

Properties
Go to game folder, right click on RDR2.exe, set checkbox "Disable fullscreen optimizations",
click on "Change high DPI settings" and enable "High DPI scaling override".
Same for PlayRDR2.exe