THIS ONLY WORKS FOR STEAM VERSION AND NOT THE CD/RETAIL VERSION
This is meant for higher spec (4 and more core CPUs) that can handle the game without arbitrary pauses in the code.
Doubles if not triples the framerate but that's if your CPU is powerful enough (especially for Ryzen CPUs that used to be bottlenecked easily).


https://www.moddb.com/games/rome-total-war/downloads/rtw-dxvk-version/

If this doesn't work, you can use dgVoodoo2. Although there have been some instances where neither option works so I have no idea what could be the cause there.

Vanilla
https://drive.google.com/file/d/1UeGcR7-VBT9qpJeEZb1LWJoXvFjg9RM2/view?usp=sharing

Barbarian Invasion
https://drive.google.com/file/d/11PdD3tRJVsQAAeTMT8WoNgjpFC-t-jo5/view?usp=sharing

Alexander (has two files, testappa is opened by Steam and RomeTW-ALX is used by mods)
https://drive.google.com/file/d/1de4Z_NAk2c-dA80N4zaAlKm1jUYKiYf7/view?usp=sharing

https://drive.google.com/file/d/1k0DCqKBekQdrVhvcn_FOE5Im-b6fPwOl/view?usp=sharing

(this is to adjust and make zooming faster with the new height limits on the camera, readme included)

All of them can be installed by dragging and dropping them in RTW folder and replacing RomeTW.exe with the patched one to install debug camera mod. To uninstall, delete dbghelp.dll and verify in game files on Steam to revert back to vanilla exe.

The dbghelp.dll file is being put in place of a debug file that has somehow been used in the Steam version of RTW without any debugger attached this entire time on top of RTW code forcing arbitrary function calls that pause the game (at the time this was necessary to not fry old CPUs and make textures/sound load properly. For context, with this mod I'm getting 30-40% CPU usage on Ryzen 3 3100 and on multiple cores too). Something similar has been used in Dark Souls' DSFix to get the game to not run at locked 30fps anymore.
By concept, this should not work with multiplayer but through rigorous network tests with 8 players inside 15k+ troop count battles, a stable version with solid (if double the fps counts as solid idk what would) performance gains has been made.
Shoutout to everyone for putting up with that one Saturday evening where 3 games crashed after waiting for 20+ minutes.

• Campaigns by themselves run smooth but camera drops the framerate to 30fps and lower on mods.
  dxvk version seems to have fixed this issue.
  
• Potential rendering/flickering issues have been reported, don't know what the cause is yet but it's likely low spec PCs may struggle with this mod.
  
• Camera stuttering may happen on larger (12k-15k+ troop count) battles Seems to happen under some dgVoodoo configurations, may have to use the prepackaged dgVoodoo config if that can help.
  
• Potential desync issues in 4vs4 multiplayer lobbies especially if non-compatibility version is used. Warn people ahead of time or if you have issues connecting to the lobby to begin with and get error with numbers starting from 12 or 6 then change to compatibility dll if you haven't yet. Fixed with latest version.
  
• FMV videos are forced to have 1ms interrupts, the dll may make them stutter as a result of breaking that so intro videos may sound choppy. A non-issue for those skipping intros, the rest of the sounds seem fine.
  
• Projectile trails on 10k+ troop count may draw slightly late as the engine's supposed to stop to draw the arrows, only really visible if you have projectile trail mods installed and a lot of archers are firing at the same time. Trail effects from rain may be slightly broken, now slightly looking like original Medieval.
  
• Cursor lag present for low spec PCs.

Need to implement a dgVoodoo-less solution,
Non-debug file dll with autohook that loads into both Steam and CD versions
Make a custom d3d8.dll/d3d9.dll file with this performance fix (d3dto9 has the source code available but I couldn't get it to work with RTW by itself)
Target specific graphics-hook32.dll function calls to maximize performance without affecting multiplayer