I know someone will come here to say the map is broken after the update, so here is an easy fix, copy your games new terrain shader(Farming Simulator 25\data\shaders) over to the map(FS25_MonteithRCR_V1_0_6RCR\mapUS\config) and overwrite the old one and bam you are good to go!
Viewing post in FS25 Monteith, IA 1X RCR comments
If it's not C:\Program Files (x86)\Farming Simulator 2025Then you've installed it somewhere else, then I have no clue, I've not used FS CD installs since 08' , you can search the forums but that's the best help I can give, unless you can find someone who has the file and can send it to you.....
Since there is an update pending then best wait.