Having served 20+ years as a director on various 501c3 boards, I'm pretty familiar with the requirements of the role. Fundamentally, directors have the duty to serve the interests of the organization vs. the interests of directors. This quote [0] sums it up succinctly:
Board members are the fiduciaries who steer the organization towards a
sustainable future by adopting sound, ethical, and legal governance and
financial management policies, as well as by making sure the nonprofit has
adequate resources to advance its mission.
So yes indeed, board members serve with the burden of explicit fiduciary duties to the organization.
[0] https://www.councilofnonprofits.org/running-nonprofit/govern...