It’s all fly by wire nowadays so there aren’t any cruise modules or extra parts or relays to go bad.
Do you have a check engine light? Some codes will disable cruise (coolant or other temp related stuff I believe)
If no lights then it’s likely user error. I usually am unsuccessful at turning on cruise in my wife’s car. It happens, and it doesn’t mean you’re dumb.
I dug up some old dash pics from my phone
You want the little speedometer icon with the arrow and the speed in the bottom corner like the top pic. This means you’re cruising.
Speedometer and - - means the cruise is on but has been canceled with the brake. His (res) to resume
I’m not assuming you’re incompetent, I’m just trying to help. There is always the chance that there is something wacky going on with your truck but I have to assume the truck is working fine since you provided little info.