I have the exact same issues on two separate pcs of similar builds.
Specs:
AMD Ryzen 3900X 12c/24t 3.8ghz
64GB DDR4 ram (can't remember speed)
Radeon 5700XT / GTX 2070
the card is the only real difference, both machines have awful frame rates on haven and hearth. Talking low 30's when walking around my village. the game never utilizes any of my cpu or GPU past 2% and 10% on both machines.
Its literally just haven and hearth that is shockingly bad for performance, all other games running amazing on both machines. Can't even blame it on java since minecraft runs just fine at well over 100 fps too