I really don't think they reduced texture or 3d trees. My post on textures was about the ps4 version.
Some tracks are ports from sport with minor changes . Brands Hatch for example only has like 5 3D trees on GT sport , they are all found aroound the first hair pin . No idea if they added more in the ps5 version but judging from replays the track only got better textures and grass added to it on both ps4 and ps5 but the trees were left untouched . Same goes for Sardegna road and dragon trail . Susuka Reamains unchanged minus better textures on all versions. I doubt they touched up any of the ovals or tokyo tracks either.. What im trying to say is i doubt this was downgraded via patch but has always been like this since day 1 , Mind you on base ps4 kyoto , willow springs , Alstice ,Route X and Mt. Pamorama ALL got upgrades graphicaly .