There are a few servers. For now, they are all private (due to abuse). If you would like to connect to them and I know you from personal life or work, I can add you to the whitelist. If I only kinda know you, I could still add you on if you seem okay. If you would like to add some people you know, I can add them too.
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OG server vanilla
Server version 1.21.8
og.mineraft.diyarciftci.xyz
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Allthemods 10 server
Server version 1.21.1 (Server 4.14)
atm10.minecraft.diyarciftci.xyz

Follow relevant guidance for client flags to improve performance:
https://allthemods.github.io/alltheguides/help/java/
As of time of writing, current recommended for those with 12GB+ RAM is this:
-XX:+UseZGC -XX:+ZGenerational -XX:+DisableExplicitGC -XX:+AlwaysPreTouch -XX:+PerfDisableSharedMem -XX:+UseDynamicNumberOfGCThreads
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