Tuinity VS Purpur

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)

We will be downloading the Minecraft server files into this directory. To preface, there are numerous variations of server JARs that can be used (e.g. Spigot, Paper, Purpur each touting their own benefits). For this tutorial, we will be working with Paper, a fork of Spigot that is optimized for performance.

I Mostly Like Linux as a OS For a Server and PurpurMC (https://purpurmc.org) As a Server Software and i Mostly Use EssentialsX and WorldEdit and More Server Management Stuff.

If you prefer to go the old-school Bukkit/Spigot/Paper/Purpur route (which provides the greatest level of compatibility with pre-existing server plugins), I recommend the latter of the four. Each of these projects is a fork, built on each other in that same order. Each fork offers additional customisation, API, and performance enhancements over its predecessor.

I’d recommend Paper (which is a fork of spigot) or Purpur which is a fork of paper and pufferfish

If you're looking to re-add gravity duping I would recommend not using a plugin but switching your server software to PurpurMC. It is a fork/version of PaperMC that re-adds gravity duping as a config option as well as the ability to toggle back on things like tnt duping and several other features that the PaperMC devs arbitrarily decided were bugs (even though Mojang has explicitly not removed them).

Small addendum:\ If you want to keep using a paper derivative (as a drop-in replacement), you can use purpurMC instead. It provides a config option to enable gravity block duping by disabling sand.fix-duping. (At least for sand)

You can host a small purpur server

Have you tried re-downloading the latest purpur jar file from the purpur website?

tweak some configuration, try lower your entities spawn, I at last you might want to try PurPurMC for the server, it's paper fork with some modification, I feel a lot of improvement since using this fork...