Hello Aternos team, I did read that plugins that aren't in bukkit wouldn't be accepted, but the mod author of slimefun has ceased to upload there due to him working on another project, but I found out that he still does some experimental builds on github from time to time, and I found a build that works on 1.14 which is the version I'm playing on.
The bukkit page for the plugins is the following:
Slimefun bukkit, but then you would need to scroll down to Development Builds, then select Build #96 (The one I was able to make work).
For CS-CoreLib (Mod from the same author, required to run Slimefun) in the bukkit you go down to Source Code which leads to his github, then go to Development Builds and get Build #39.
I understand that it breaks the terms but I would be eternally thankful if these plugins became available, but if you really are unable to proceed, no problem at all, I understand the problems that may arise with unofficial builds. Thanks in advance, have a great day!