You can follow the steps in our guide to learn how to set a custom resolution you want in the game.
How to Set Custom Resolution
To set a custom resolution that is higher than what you are able to select inside the game, you have to edit three .ini files that are inside the game’s folder
(ie. C:\Program Files\SteamLibrary\steamapps\common\Command & Conquer Red Alert II)
The three files you are looking for are:
DDrawCompat.ini
RA2.ini
RA2MD.ini
Step 1
First, you have to put in your resolution in the first file (DDrawCompat.ini). Open it in the text editor put in your resolution at the SupportedResolutions line. So for example, it could then look like this
SupportedResolutions = 640×400, 800×600, 1024×768, 1920×1080, 2560×1440
When you are done, save it.
Step 2
Edit the second file (RA2.ini). The lines you are looking for are
ScreenWidth=800
ScreenHeight=600
Edit these two lines and put in your resolution. So for example, it can look like this:
ScreenWidth=1920
ScreenHeight=1080
When you are done, save it.
Step 3
Repeat step 2 for the last file RA2MD.ini and you are done.