Alright. After looking a bit I think I found out the problem.
On logs it gives an error message where it says "The plugin could not be enabled, possible solutions: remove the plugin or install a different version.".
I don't think this problem is related to Aternos. I'm thinking since 1.19 just launched it's probably very early on and people haven't updated the plugins yet. So if that's the case I guess i'll just wait but if not then i'm not sure.