I can't see him doing the "flip-the-bird" option, but I also can't rule it out.
Manchin has a very conservative constituency to appease in WV. We're damn lucky just to have him as (D) frankly. And in the past six months we've seen him back most of Biden's major measures, ones that were necessary for him to vote yes on. The Voting Rights Act can't be passed with Reconciliation, so Manchin coming out against it makes sense - he appeases his conservative voters, and doesn't impact significantly.
The big ticket item, as we all know, is the filibuster. Right now he's "against" it. But there is room to maneuver since the GOP blocked the Jan 6 Joint Committee bill (interestingly, two Dems actually missed the vote - not just Sienna - but it would have still fallen short). The infrastructure Bill is coming up soon, and it has bipartisan backing. If it doesn't pass, even after a bipartisan team of Senators worked it up, that might be the straw that pushed Manchin-the-Camel over.
And, to be clear, I'm exceedingly frustrated by all this bullshit maneuvering. Pisses me off when there is so much to be done and everyone is taking their sweet time. However, it bares remembering, these same shenanigans kept the ACA from being fully repealed back when the GOP had control.