I'm also having this related problem too. I have a PC that runs a I5 9400f with RTX 2060 and 16 GB of RAM, I downloaded a texture pack where the items are high quality. Every time when I joined my world and put the texture pack in, it run smoothly at first until when I grabbed out a random item and put it in six item frame, my FPS drop badly from 165 to 20 FPS and that's nuts considering my PC is able to handle these type of graphics. I asked my brother who has a potato I5 with 8 GB laptop to join me and he did, but the lag didn't affect him and he seem to run pretty smoothly with 60 FPS. I tried it on many devices, including my IPhone I have Minecraft on also, and they all run smooth compared to my PC. I don't know if the cause is the update or rendering of some sort, but it does take up a lot of my memory usage. Reply to me if anyone are having the same issue and we can try to figure it out.
WeAreCraft
I'm also having this related problem too. I have a PC that runs a I5 9400f with RTX 2060 and 16 GB of RAM, I downloaded a texture pack where the items are high quality. Every time when I joined my world and put the texture pack in, it run smoothly at first until when I grabbed out a random item and put it in six item frame, my FPS drop badly from 165 to 20 FPS and that's nuts considering my PC is able to handle these type of graphics. I asked my brother who has a potato I5 with 8 GB laptop to join me and he did, but the lag didn't affect him and he seem to run pretty smoothly with 60 FPS. I tried it on many devices, including my IPhone I have Minecraft on also, and they all run smooth compared to my PC. I don't know if the cause is the update or rendering of some sort, but it does take up a lot of my memory usage. Reply to me if anyone are having the same issue and we can try to figure it out.