Technic Launcher -> After Humans Modpack -> Open to Lan (Server via VPN) -> Extremely poor performance

[ACX_DeusVult]

Hello everyone,

after years of playing no minecraft i wanted to try another round with my friends.
Sadly, the performance issues are still a thing. Last time i rented a Nitrado server and was pretty disappointed, it ran the After Humans modpack pretty laggy, everyone had nearly constantly under 60fps, sometimes under 20... and all this with very (very) powerful desktop computers.

So, for this time, i thought "let's get rid of chainlinks, make the chain shorter. No server menas probably less lagging and on top my desktop computer has way more power then any of these rentable servers."... Well, i guess that server was not the problem at all.
As soon as the technik launcher was downloaded and "installed", i opened the options. it was already set to allocate 16gb of ram. And boom, the startup of minecraft was laggy, the world creation was laggy, the spawn was ultra laggy and playing in this world with four guys is laggy all the way.

Here are my specs:

Operating system: Microsoft Windows 10 Pro x64 21H2 (Build 19044.1826)
Java Version 1.8.0_333-b02 64Bit (including entry in the PATH variable pointing to it's bin directory and also the two other variables JAVA_HOME and HO_JAVAHOME)
Processor: AMD Ryzen 5950X 64MB L3 Cache 16x4,7GHz watercooled (Push-Pull, 6x 120mm Corsair LL-Series)
Mainboard: Asus ROG Strix X570-E Gaming
System SSD: Samsung 980 Pro 500GB (This is where Appdata -> Minecraft / Technic are located, too)
Video Card: Asus SROG Strix 2080Ti Advanced
Random Access Memory: G.Skill 4x32GB DDR4 3200MHz CL14
These Components are located in a Bigtower Case with a whopping additional 6x 140mm Corsair LL-Series
Power Supply Unit: Be Quiet Dark power Pro P11 850W

The System runs pretty much every game on this planet with ease and maxed out to hell and back.

But Minecraft... it scares the **** out of my rig.

I've read some different forum threads before posting here, so i know Java is bad, has a pretty bad garbage collecting thing, more RAM = more FPS is a myth, and so on...
But i have not really found an answer to my question. My question is simply: What can be done to increase performance?
At the moment, i am opening a singleplayer world, opening it to lan afterwards, let my three friends join via VPN. The connection is quick and easy, once the loading process of the world is done.
But the performance on the "server" is pretty whacky. So it goes up to hundreds of fps one time, then drops to 12 fps while i can not sense ingame happenings like a massive mob farm or something likely to trigger such frame drops.
My three buddies experience the same things. They all have systems i built for them (yeah, i'm the IT guy in the group...) with pretty good stats. i7 to i9, 32GB to 64GB RAM, only pcie NVME m.2 SSDs, etc...

So, my first question would be: What to do within Java settings before even starting Technic launcher?
My second question would be: What to do within the settings of the Technic launcher?
My third question would be: What to do within the game settings (mixed with the mod settings of forge / optifine / etc. that alter the original settings)?
My fourth question would be: Can i do additional prerequisites? Is there some NVIDIA stuff that i can / have to alter in order to recieve more frames / more stable framerates ingame?
My fifth and last question would be: Is it possible AND does it make sense to create a modded Java server .JAR with all the mods from the After Humans mod package and run the server locally but in an separate console / gui like i can do with the vanilla one and does this in any way increase anything?
Ok, i lied to you, shame on me. Let's call it bonus question: Is there a newer version / variant of this modpack or a modpack nearly identical by means of it's contents, that maybe has lesser performance problems?

Thank you for your help in advance.
Please don't judge my Englisch, i am no native Englisch speaker.

Have a nice thursday evening and a great start in the weekend tomorrow.
Greetings and kind regards!

Deus