i've red somewhere that it was also allowed in the community section, if so please send the one that is allowed.
What was the name of that plugin that shows a pop up window with rules after you join?
I believe there are a few, you can find most of them by searching keywords in the plugin search page.
I use Server Info
https://umod.org/plugins/server-info
The plugin you mean is called "Rules GUI"
Search times on Google for "Rules GUI" Then you should find it very quickly.