It's a ton of work, especially with the number of systems - you've got combat, resource management, settlement development, food managment, espionage, diplomacy etc - these all need to play together well. And then you've got to add in the storyline, graphics, marketing -but I think I'm making pretty good progress.
I'm still using Unreal Engine 4 because I started work on that version and I haven't needed to upgrade to 5 since it's been released. I've got a free prologue that I'm releasing on October 1, so now until then is a lot of polishing to make it work well.