This is a guide to making the campaign in Command and Conquer 3 run at 60fps (or even 90fps), using a paid method. There are two real options, both quite cheap (less than $7USD). Command and Conquer 3 runs at 30fps by default, and this cannot be changed normally without affecting the game speed. The two options I present here will overcome that issue and allow 60fps gameplay in the campaign.

There is a free mod to run the game at 60fps, however it does not work for the campaign, only for the skirmish mode. That mod can be found here:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3018365845

If you are playing the campaign, it is highly recommended that you follow this guide to restore balance changes to the campaign, it is much harder without it:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2766487170

Unfortunately there does not seem to be a free way of playing the campaign in 60fps, hence this guide. There are two paid options, the first of which is the Sage Meta Tool mod, which can be found here: https://www.patreon.com/posts/sagemetatool-53702342
With more info here: https://github.com/MetaIdea/SageMetaTool
You will need to sign up for a $6USD membership, which you can then cancel once you have access to the tool; it will work forever once activated. I have not used this tool so I don't know how well it works. It is limited to Sage engine games, which include the Command & Conquer games and Lord of the Rings Battle for Middle-earth games. However it also includes quite a few other features such as unlimited zoom and different camera modes etc.

The second way is to use a Steam program called Lossless Scaling, found here for $6.99USD:
https://store.steampowered.com/app/993090/Lossless_Scaling/
This tool will work for almost any game, so it is the better choice in my opinion if all you are after is 60/90fps, or even higher with other games that run at a base framerate of 60 or more. It was originally designed to upscale games, however it has also added frame generation (x2 and x3) which should work with any graphics card.

Normally you would need to force games to run in Windowed or Borderless Windowed mode to be able to use Lossless Scaling, however it works just fine with C&C3 as is. All you need to do is:

1. Open Lossless Scaling
   
2. Set Frame Generation to LSFG 2.2
   
3. Set the Mode to X2 (for 60fps) or X3 (for 90fps)

Then once you have opened C&C3, press the Lossless Scaling hotkey, which by default is Ctrl + Alt + S, and the framerate should immediately double or triple depending on what Mode you set. Note that the Steam FPS counter or other overlays won't detect the added frames, but Lossless Scaling has its own FPS counter that shows both the captured frames (which should be 30) and the adjusted framerate (which should be 60 or 90). The game should immediately feel a lot smoother.

If you experience overbright washed out colours, enable HDR support in Lossless Scaling under the Rendering section.

Lossless Scaling should work fine with the other C&C games as well; however you may need to force them to use Windowed or Borderless Windowed mode.

Hope that helps!