quilt-serverside-mods VS Purpur

not a jobs one, no. you can check out the serverside mod list here https://serverside.infra.link/

Have a look at this list. It's got a ton of useful server-side mods which you can use on your server.

To be honest, the natural path for those that come from Bukkit and derivates for the future is to either switch to datapacks, migrate altogether to Bedrock (that already have interesting advances on its addon/pack system) or switch to Fabric server-only mods - There is a lot of possibilities already and there is also Polymer project that aims to "convert" some classic mods to server-side-only, so at the end maybe OP should look at it all and forget the Sponge thing.

This seems like a decent shop mod, for a larger list of mods you can look here. Another shop mod I found was https://modrinth.com/mod/diamond-economy

Once you have your server OS installed, look through the performance section of Quilt Serverside Mods (even though it says Quilt all the mods are Fabric compatible). Also make sure to set sync-chunk-writes to false in your server.properties.

I have been using this list to find some optimization mods but some mods in the performance sections seems to break the game (eg - Very Many Players ).

Here’s a good resource for server-side mods, some of them are for quilt but quite a few are fabric mods (originally the list was only fabric mods, also quilt is a fork of fabric, so if you wanted to give it a go, it has most of the same benefits fabric does)

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...