Both ideas make sense though.
Either Jar Jar helped the Sith to rise to power or he is Darth Plageuis.
If he actually is Darth Plageuis then maybe he just did not want to be officially recognized? Think about it, it makes sense. Why put yourself on the throne when you can put someone else on it, that does practically everything you do? Palpetine is Jar Jars puppet.
Maybe he did not even know or notice that he is a puppet? Maybe Palpatine did not know that Jar Jar is Darth Plageuis...
And tbh, the whole prequels and practically all Star Wars movies suddenly become much better with Jar Jar being a Sith in control of everything.