I cleared the star chart, finished every story quest, maxed out open-world standings (except PoE), maxed out syndicates (New loca, The Perrin Sequence, Red Veil, Steel Meridian), and killed Archon several times.
I genuinely don't know what to do from now on. Every other weapon feels like a downgrade of incarnons. I'm unsure whether I want to farm other warframes and do that tedious forma routine again.
You pretty much are at the point where you can do anything "Comfortably" or just Play something else without feeling like Missing Out on here. I was there too, and I just kept striving for things that interested me, like making a Zaw with a certain theme (Which now is my most played Melee) or getting a Riven for my most used Weapons, Making my Main Warframe viable for any Mission, you get the idea. Setting goals out of pure interest is my suggestion