Biden pivoted the US' middle east strategy towards appeasing Iran as opposed to Trump's method of isolating the mullahs. Bad actors immediately picked up on the lack of the US' pushing for more Abraham-like accords as an opportunity to act in the new envrionment...and have.

If anything, had Biden actually done that, it would have made an attack less likely. Again, the primary impetus for Hamas' strike was the continuing expansion of diplomatic ties between Israel and the Saudi-led coalition, combined with (ostensibly) the lack of progress towards a Palestinian state. Those trends began under Trump, and would certainly have continued at least as much in a second Administration - if not more, as you suggest. Having Trump instead of Biden wouldn't have made a Hamas attack less likely, but more.

But we didn't really reverse course on those things. The U.S.' continued support for more Abraham-like accords in the area, and trying to foster greater regional ties among Israel and the other anti-Iran players, kept the pressure on Hamas to do something before Israel was no longer vulnerable.

But it's folly to say that the absence of US resolve and leadership have no effect.

No, it's not. Sometimes we're just not a factor. Much more often, who the President is is not a factor - because even though Presidents have different foreign policy positions at the margins, the core position of the U.S. towards most other nations only changes within a narrow range. At the end of the day, at 30,000 feet the U.S. foreign policy in this region that Hamas would base their decisions on is "Israel good, Hamas bad" - they just don't have any intelligence assets or other resources that would allow them to form much more of a strategic parsing of what U.S. policy about Hamas would be.