tic-tacs VS Tuinity

Starlight performs substantially better than phosphor and greatly speeds up terrain generation. Krypton for networking performance. C2ME or tic-tacs (both aim to do the same thing and are not mutually compatible) greatly improve world loading and terrain generation but are experimental and, in my experience, not compatible with a lot of other mods. Dimensional Threading puts each dimension on a separate thread, but also tends to not be very compatible with other mods. FerriteCore aims to reduce ram usage. This page has a whole list of mods.

Could also pregenerate your world with chunky. To make it quicker add Starlight, Lithium, tic-tacs(This might be incompatible with some worldgen mods, but it massively speeds up terrain gen speeds if it works), and Carpet(use the "/tick freeze" command to freeze the game so there's more resources for terrain gen). Then switch to a paper style Tuinity server and set the worldborder to keep people from moving past pregenerated chunks.

Tic-Tacs for world loading

I would recommend a fabric server running krypton, lithium, starlight, tic-tacs, hydrogen, and ferritecore. Those mods are geared towards optimizing chunk generation and loading while having 0 impact on vanilla game behavior (the last two are geared for reducing ram usage). Of all the performance mods I've messed around with, those are the ones that I would recommend most. You could also add carpet and set it up to add tps to the tab list if you want to easily see that number.

tic-tacs is an absolute must as it dramatically improves chunk load times

Also try Tic-tacs (can cause some issues).

And also run Tic-TACS which replaces Minecraft's clunky chunk loading engine for a multi-threaded awesomeness. This is the most experimental of the bunch, and the least recommended for any kinds of critical usage.

tic-tacs

Could also pregenerate your world with chunky. To make it quicker add Starlight, Lithium, tic-tacs(This might be incompatible with some worldgen mods, but it massively speeds up terrain gen speeds if it works), and Carpet(use the "/tick freeze" command to freeze the game so there's more resources for terrain gen). Then switch to a paper style Tuinity server and set the worldborder to keep people from moving past pregenerated chunks.

You can try out Tuninty for extra performance

Tunity - Github Repo - (no website)

Strip out all plugins, make backups of & reset your yml's. Does the bug still occur after doing that? Then report on their issues tracker: https://github.com/Spottedleaf/Tuinity/issues

Tunity: https://github.com/Spottedleaf/Tuinity

Tuinity is a fork of Paper that includes optimizations that are generally tailored for servers with high player counts. It also includes Starlight: a complete rewrite of the lighting engine which greatly improves the speed of chunk generation. One benchmark has shown that Starlight can generate light 35x faster than vanilla.

Tuinity

For server jar I would recommend using Tuinity (or maybe even Purpur). As Tuinity has some more optimizations that help for larger servers and Purpur is a fork of it that I believe has even more experimental optimizations.

https://github.com/Spottedleaf/Tuinity/blob/master/patches/server/0061-Rewrite-the-light-engine.patch here is the patch, at the top he writes a description that can help you read more about it.

Use Tuinity (it's a fork of Paper, optimized for higher play counts)