NeoForge
Minecraft with NeoForge mod loader
One Main Thread
The world tick runs on one main thread, so per-core speed matters more than core count. More RAM only helps until the server has what it needs. Past that point it can cause longer garbage collection pauses. Real gains come from lowering simulation-distance and view-distance, pre-generating the world (for example with Chunky), and profiling lag with spark.
Minecraft 1.20.1+ Only
NeoForge only supports Minecraft 1.20.1 and newer. For older MC versions use Forge.
Server Mods vs Client Mods
Players need the same Minecraft and NeoForge version, plus every mod that runs on both sides, in matching versions. Client-only mods (shaders, minimaps, Embeddium, Oculus and similar) must not be uploaded to the server. Remove them from your modpack's mods folder before uploading, or the server will crash on startup.
EULA and RCON
On first start the server stops and asks you to accept the Minecraft EULA. Read it, set eula=true in eula.txt from the file manager, then start the server again. RCON uses the password and port from your Startup tab. You don't need to touch server.properties.
Official Documentation