Let's offroad / mountain bike / mtb / ride dirt

If I was looking to ride light trails that aren't too technical but quite muddy, I would get the most modern and expensive bike I could that was design to ride light trails that aren't too technical but quite muddy

Fixed that for you!

I think virtually everyones opinion on this will contradict your own. So if you don't want a modern short travel full sus xc bike then a 15 year old bike is the answer.

But I'm not sure how a bike like that will feel any better than whatever 27.5" bike you have right now.