I'm not very familiar with how modpacks work, but my guess is it has something to do with your computer. Max render distance, fancy graphics, 4K resolution, no problems for me. But if someone else have a better guess on why your performance is poor, listen to them instead because as I said, I'm fairly new to modpacks.
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I AM NOT YOUR PERSONAL MINECRAFT MOD SUPPORT AGENT, SO PLEASE DO NOT PM ME ABOUT PROBLEMATIC MODS THAT ARE NOT MINE. If you're having trouble/crashes with a mod, you'll have better luck resolving it in this forum section than PMing me. If you already made a topic, be patient about responses. If you have troubles with anything non-Minecraft related on your PC, I might be able to help, though, but no promises. Even though I could wish to be, I'm not a wizard.