If you got stuck like me trying to get DLDSR or DSR to work with Vegas 1 use this.

Download this - https://community.pcgamingwiki.com/files/file/103-tom-clancys-rainbow-six-vegas-resolution-patcher/
The config that says "EDIT* (here is the file for 2560x1080p edited with Hex Editor)".

Open the config via HXD and find "00 0A 00 00 38 04"
00 0A = 2560 (x axis)
38 04 = 1080 (y axis)

Replace these with the resolution you want from https://www.wsgf.org/article/common-hex-values
Use the formatted values.

If you cant find your resolution, google a decimal to hex calculator or just use this https://www.rapidtables.com/convert/number/decimal-to-hex.html

Use Hex signed 2's complement value and re write it like 12 34 => 34 12

So with this any aspect ratio or resolution will work with DSR or DLDSR.

One last thing, if you are stuck at 60 fps in game on a high refresh monitor after using this, change your resolution and refresh rate to the one you want in your gpu control panel then launch the game. Then change back after playing. Also, don't change the in-game resolution, leave it as is.