Plugging Orphan Wells and Environmental Restoration Act of 2021 or the POWER Act of 2021 This bill addresses orphaned, abandoned, or idled oil and gas wells on federal, tribal, state, or private lands. Specifically, the bill reauthorizes through FY2026 the program to remediate, reclaim, and close orphaned, abandoned, or idled oil and gas wells located on federal land. Additionally, the Department of the Interior must establish a program to provide grants to states and Indian tribes to remediate, reclaim, and close orphaned oil and gas wells located on state, tribal, or private lands. In providing grants, priority must be given to states and Indian tribes that already have an established program to carry out such activities. Finally, the Department of Energy must provide technical assistance to oil and gas producing states and Indian tribes to ensure practical and economical remedies for environmental problems caused by orphaned or abandoned oil and gas well sites on state, tribal, or private land.