SMAAT2X

I have not found SMAAT2X anti-aliasing anywhere, so please make someone do the anti-aliasing as in CODMW2019

SMAA T2X includes a temporal postprocessing filter, which is too complicated for ReShade community to code. I mean, theoretically, it could be done on a game-to-game basis, but it is basically almost like writing a new shader for each individual game. No one would really do that unless they're particularly obsessed with a specific game.

I was looking for such anti-aliasing for RDR2

According to the SMAA.fxh header file SMAAT2X (also known as Temporal SMAA) is only possible when SMAA is implemented directly within the game's own render pipeline as it requires the game to be performing 2x MSAA and then allowing SMAA to run against both individual MSAA samples in order to generate its sampling data. As far as I can understand from the code this is simply not possible via an injected post process shader alone; you can enable 2xMSAA in the game if the game lets you, but the injected SMAA code will not run until the game has completed fully rendering the frame, including having performed already both MSAA passes.

SMAA T2x is temporal only, it doesn't need MSAA to work.

SMAA T2x, for little additional cost, offers a very attractive
tradeoff for any kind of rendering engine (deferred or forward),
avoiding 2x multisampling while still reconstructing
subpixel detail.

I think what you meant is SMAA S2x Here are all the variants, taken from the original paper:

SMAA 1x: includes accurate distance searches, local contrast
adaptation, sharp geometric features and diagonal
pattern detection.
SMAA S2x: includes all SMAA 1x features plus spatial
multisampling.
SMAA T2x: includes all SMAA 1x features plus temporal
supersampling.
SMAA 4x: includes all SMAA 1x features plus spatial and
temporal multi/supersampling.

It would still need motion vectors but we already have a few shaders exactly for that. For example MartyMcFly's and Jakob's motion vector shader.
Is there any other obstacle for it's implementation?