How's biking in US outside of big cities? Cause it's the best place to bike in my country (Poland).
You just leave the city and turn to any random small road and you can relax. My favorite are the farming land near Lublin. 30 minutes from the city center there are roads where you pass 1 car per hour :)
For bike trails, there is an effort to connect Maine to Florida called the East Coast Greenway: https://www.greenway.org/
Having used it myself, it's not continuous but certainly better than nothing.