My server runs fine with more than 10GB of RAM
but when I added fetcher suddenly stuff stopped working well
When I gave my self op permission, this is what I saw

Fetcher keeps on detecting what items are in my backpack and it made my tps drop like crazy, and when I gave myself op I can't even send a message because everything flashes by since my message box was flodded with fetcher's detecting updates.
I mean, why do you have to update like every 0.05 seconds???
I hope you'll fix this soon since I can't even find the datapack in my server now LOL
(Also the Chinese translation isn't complete although it's supposed to be, but I'll translate the untranslated parts for you guys)

This looks like a mod issue. Command block output is disabled in the map and will never show up when everything is working properly.

The recommended setup on the server side is Fabric with Lithium for best performance. You can also run vanilla.

Note that especially Paper/Spigot (even with no plug-ins installed) is known to mess with datapacks and breaks things in subtle ways.

Client-side mods do not matter when joining a server, but they could be problematic when playing single player.

and another thing, as soon as I entered the /function fetchr:game/end command, the tps became normal like this

Oh and my version of fecher is 5.1.1

Ohno I can't remember the password to my server LOL
I'll try fetcher on my friend's realm.

Last time I checked, realms did not support worldgen datapacks.

They did a recent change were experimental features are available on realms now, but not sure if that also allows for worldgen packs now.