Something vaguely Indiana Jones-like. Archaeological expedition discovers something that has galactic ramifications which ultimately lands him back into a meaningful role at Starfleet and reuniting with select TNG era figures along the way.
Space Cowboys! - the Star Trek version. An old threat only Picard has ever managed to settle returns (maybe the Sheliak? Or, if we're feeling uninspired, the Borg), and the "new guys" in the Federation are incapable of handling the situation on their own, so they dust off the "dinosaurs" that came up with a solution many years ago, and throw them back into action to return for a last hurrah and save the day a last time.
I'm not interested in seeing Picard in command of any ship or group of ships. Especially not the Enterprise. He should be in a very different place from where we last saw him. For me, personally, that means either a diplomat, a civilian or a political leader. Yes, technically, Academy commandant would be very different, but just ugh to an Academy show. If they want to do that kind of story it should be completely separate from the return of Patrick Stewart. I don't have major preferences in terms of specifics for any of these possibilities, but I do not want to see the Irumodic syndrome (at least not as the primary plot point) because Stewart's already given that performance in Logan (and stretching it out over a whole mini-series/series would be too much, anyway). I also do not want to see the Borg in any way shape or form, ESPECIALLY not as potential Federation members. That's like Ebola petitioning to be a US State.
As a more serious response to the OP's premise I would like to see a 10-episode Logan-style story, where Picard is facing his mortality and has one last mission in him. If possible, I'd like the mission (whatever it is) to be about him, not about "saving the whole Federation" (he's done that many times already). A small-scale, intimate character study where Stewart can flex his acting chops, with only glancing references to TNG as a whole (they should, by now, have all moved on to other phases of life) and only one (at most two) TNG characters with any significant presence. Of course, none of this will happen--but it's what I'd like to see.
Stripped of rank and seniority, Ensign Picard has to redo decades in Starfleet to get his retirement. Serving on the Enterprise F, under Captain Nog.
My vote for the theme is as follows. To the tune of "The Muppet Show": It's time to for tea, Earl Grey, hot, Turn on that inner light, Data will try to train Spot On the Picard Show tonight. It's time to vent the coolant, It's time to make it so! This is not called 'Reliant', But instead the Picard Show! Cmdr. Tomolak: "Why do we put up with him, for days and also nights?" Gul Madred: "Perhaps I'll start some torture, and make him see five lights!" But now let's get things engaged! This is not Discovery, We're hoping to see Riker, Beverley, Please, God, not Wesley! And other old farts on Picard's Showwwwwwww!