As others have said, it probably doesn't matter much as the spec requirements are very low, especially if you are willing to turn the graphics down a little.
One thing to consider is that Civilization is CPU bound (unlike most other games which are GPU bound). The better your CPU, the faster those late game turns will process. This is also the biggest practical limit to large maps with lots of players on any modern machine. So, if you buy a notebook it'll almost certainly be using an integrated gpu which limits the power of your cpu in a number of ways because they share resources and heat limits. An older cheap desktop is probably the most cost efficient if you play large maps, and a cheap notebook is probably most cost efficient if you don't. I play standard and small games on a 4 year old $400 Ryzen-5 vivobook, but then switch to my PC if I'm going to play anythign bigger.
But again, it mostly won't matter. You can go pretty cheap and it'll be fine.