Perhaps a command that allows you to flip gravity, like the up down and all around mod. It can use @p and @a so you can flip gravity only for certain players. 1.16-1.18 compatibility.
Do note that modded servers and plugins don't work together. Keep that in mind when building your stuff.
This is technically incorrect since there is software such as Mohist for this, but some plugins and mods are incompatible with it and also it's not the most stable thing to run a server on - But it's defenitely doable, I've done it before on multiple different versions Also it's not updated to 1.19 yet, but that could happen - Also 1.18 works fine obviously and most mods don't even support 1.19 yet afaik
Which we are not and it often breaks / errors. If you use it people are gonna ask for support with it which nobody is willing to give.